I render that argument valid.
but
"With HL2 they released information far too early"
This isn't the case for Ep3. 4 years have passed.
I do however agree that they will say something when the time is right, but a try doesn't hurt.
It has to be spread :D
Anyway, your theory makes sense and I support it.
You have my respect for taking the time and doing research and all. Maybe it should go to Gabe.
http://www.thesixthaxis.com/2010/11/20/rumour-left-4-dead-3-at-vgas/
edit: There is also a QR code, shown just for a split second! It redirects me to this:
http://mm.mtv.com/avTWzR
This is the image:
Notice the 1 of 3 from the bottom, right corner.