I don't know in general. I can tell you that my particular rig sleeps just fine. Originally, it had a problem waking up, but that was the OS's fault. Win7 seems to do a Hybrid Sleep by default, writing a hiberfile and then going into sleep mode. The idea is that you can wake if everything goes right, or recover from hibernate if there is a problem. But the system would never wake from sleep.
Easily solved by disabling hybrid sleep (I'll look up the details if you want; it was not glaringly obvious but somewhere in power settings). Now my machine will sleep and wake.
I have no idea if this is related to what you heard or not, though.