What a stupid reason! Competing platforms is awesome! It is probably the only reason we're getting awesome deals. Think what it would be like if Steam was the only player on the block. Do you really think we would see all these sales?! No. Valve would have no reason to do them.
Lack Of Split-screen
FFS, split screen is a console thing goddammit! If you want split-screen go play Need For Speed on a ruddy console.
"The present is a veil between anticipation and horror. Lift the veil... and madness may follow." source