Now, I have a feeling that the OEMs don't actually manufacture the glass. They source that from a glass manufacturer and have it made to their specified tolerances, but finding out which brand to get might be tough.
You're actually right. OEM in the "glass world" has nothing to do with the auto manufacturer's logo. PPG and some of the others are OEM glass companies, meaning they produce the glass for Honda/Toyota/GM/BMW/Ford/etc and their offerings meet the same specs as the dealer glass. Their offerings should be exactly the same as the offerings from the dealer's parts department, with the exception of the logo. The price is in between the glass carrying the auto manufacturer's logo and that of replacement manufacturers (used by Safelite, etc.) who use 3rd party glass (aka OEE.) OEE, original equipment equivalent, are the ones which have a low price tag and generally are inferior to the original (thinner.)
Something important to remember: The dealers won't accept OEE glass on lease returns, but will accept OEM glass and dealer glass. OEM glass also keeps the car qualified for most Certified Used programs.
Some states do have a glass law. In Kentucky, there's zero deductible if you have full coverage (regardless of your comprehensive deductible amount) set by state/commonwealth law. A few other have this also. I wish Louisiana did, as my 07 Accord got a crack less than 6 months after buying it new. I'm in the process of it being replaced, just haven't decided on the one I'm using. Still researching it, but it'll probably be PPG.
PPG supplies a lot of Toyota's glass, but this can change depending on the model and year:
http://corporateportal.ppg.com/NA/OEMGlass/40_AutoResourceGuide/Vehicles.htm