Products that can't rely on standards love this aspect of Apple. In most situations, hardware companies don't have to test their products on every board available on the market. Standards keep things in balance. If all motherboard companies make their products with the PCI standard, Hardware Company X only has to test their board once. If it works there, it'll work anywhere.
Standards are what make the computer industry go.
If you have a modern day computer, you can walk into any store and buy RAM that will work reliably. Apple has long been the ugly duckling of the computer industry. This was because developers had to make two separate products to get the Mac market. When in competition with another business, trying to meet demand, or even just trying to stay alive in the market, spending twice the money on a single product isn't always possible. Even if a development team did put in the time to make a Mac version, the market was so small that the profits were rarely worth it.