You must be young. I still remember back when Gates was talking about making ACPI a black box (unfortunately it still is, I can see) so that no other vendors but Microsoft could use the power interface. Some companies (like Intel) are pretty good about these types of specifications. I still have an Intel desktop/workstation board on my main computer at home and it has no problems sleeping and waking up.
I have had, unfortunately, problems with some other manufacturers doing the same thing - like Asus. (By the way, this isn't strictly linux, I couldn't get Windows 7 to suspend/resume on certain model Asus boards.)
It most definitely has something to do with hardware vendors. If the auto manufacturers had it their way no DIY'ers would even be allowed to work on cars. Computers are no different.