Very few consumers of music gear realize the complex, difficult, ever-changing nature of manufacture of music electronics. Simply putting a circuit-board in a box and offering it for sale is not a viable possibility in the 21st century, due to a lengthy list of factors evolving from government regulations. Not only do nearly all industrialized countries have regulations and court-case precedent covering electrical safety, the issues of RFI (radio-frequency interference) and EMC (electromagnetic compatibility) must be considered. EMC is a major issue for any electronic device sold with a microprocessor inside. And the enactment of ROHS laws by the European Union in 2005 severely restricts the types of materials that a manufacturer can use in an electronic product.
Many users of music gear have complained about the near-universal use of AC power adapters, or "wall warts", to power devices such as audio processors, small keyboard instruments, and drumboxes in recent years. Until the 1980s, AC adapters were only used to power small devices that could not contain their own power supplies, such as effect pedals. The use of AC adapter external power supplies became more commonplace in the 1990s, partly due to changes in electrical-safety regulations imposed on equipment imported to or made in the EU, and due to subsequent heavier regulation in other countries as a result of the EU's regulations, which influenced legislators in countries such as Australia and Japan. The rise of the product-liability lawsuit in the 1980s as a viable "business", especially in the USA, was also a factor. It encouraged people to sue manufacturers for making "faulty" products that inflicted injury, often whether said injury was due to faulty design, or if it was the result of misuse or abuse of the product by a foolish consumer. Because juries in such cases often found automatically against large companies regardless of the facts of the case, larger firms became very "gun shy" about product safety. Smaller firms followed their lead, simply to try and avoid ruinous lawsuits.
The main issue: bringing AC mains voltages into the product's cabinet. Any electronic device that uses more than one or two watts of power usually must be powered from AC mains. AC mains power varies all over the world, complicating the design of music electronics. In the US, Canada, most of North America, and a few other countries, wall-socket AC mains is 120 volts at 60 Hz frequency. In Japan, it is usually 100 volts, at either 50 Hz or 60 Hz (some utilities in Japan use 50 Hz, some 60). In most of Europe, the standard is 230 volts at 50 Hz. In the UK it is 240v at 50 Hz. The European voltage is very commonplace throughout Europe, Asia, Australasia, and Africa. Some countries, such as Brazil, have failed to standardize. Safety is an important issue with such voltages, as all of them are more than ample to electrocute and kill an adult human, if contacted in the proper way (current discharge via the chest and heart). Wikipedia has a very good article about mains voltages by country, complete with a map showing which are used where.
Also note that the power plugs differ greatly around the world. If only two-wire unearthed power is needed (typical for small appliances), a single 2-pin plug works throughout Europe and in many other countries---the CEE 7/16 "Europlug". If 3 pins are needed for earthing, there are three incompatible standard plugs in the same area of Europe. The most common, the French/German version, is incompatible with the Italian, Swiss, and Scandinavian versions. And there are two different-sized Italian plugs. Australasia and Israel have their own, incompatible plugs and sockets. The American 2-pin plug (NEMA 1-15) and 3-pin plug (NEMA 5-15) are also used in Japan and most of the Americas--usually in countries having 120v power. The old British BS546 plug is still used in India and much of Africa, while the UK itself now uses a totally different plug (BS1363). Argentina uses the Australian plug, but with "line" and "neutral" connections reversed. Some countries, such as China and Brazil, cannot agree on a single standard. Wikipedia has a good overview of different power plugs. Thanks to Internet dealers, a company selling music gear is prone to end up selling the same gear in many countries, complicating design greatly. There is a proposal to standardize European power outlets, which has apparently failed as of 2011. This nightmare is why manufacturers have either standardized on the "universal" AC mains inlet socket
The moment you feed AC mains into a box, EU regulation EN 60950 of Directive 2006/95/EC, or "Low Voltage Directive For Information Equipment" takes over. It deals with safety in electronic "information" devices powered from AC mains. This regulation is considered to cover music electronics, analog or digital, simply because there is no direct regulation for music gear---sales figures are not sufficient to regulate, and music gear is considered "professional" equipment as opposed to a kind of "home appliance", so music devices are stuck under "information equipment". If it had been considered a "home appliance", a synthesizer would be regulated under EN60335 instead.
The complete list of EU regulations for electrical safety is here. There's a lot of regulations. Most of them are aimed at mass-produced consumer appliances. There's even a regulation for safety in "heated gullies for roof drainage". But there's no mention of music gear.
Because in the 1980s, Japanese companies such as Korg, Roland and Yamaha started to seize the market for music synthesizers, the EU demanded that those firms start meeting EU regulations for electrical safety.