If I wake my Mac Mini with Wake on LAN, it doesn't turn on the display, either. It stays in low power mode. Same if I access the Mini for Apple file sharing. It's on, but keeps the graphics off.
This is because Apple designed Lion only to turn on the display on user interaction.
If I wake my Mac Mini for Remote Mangement, the does display turn on.
The problem is how fast a hackintosh returns to sleep. It returns almost instantly, exactly because the wake reason isn't recognized.
So the problem isn't that WOL doesn't wake the display (it's per design), the problem is that WOL and Power Button isn't recognized as a proper wake reason, which makes it go back to sleep instantly.
You should check your console in Lion on the S2L and check what Wake Reason it gives you when you wake it with Power Button or WOL. If you get "?", it has the problem. If you get PWRB or PXS1 or something, then it works as it should.