"Steam never did timed exclusives" actually isn't true:-Steam was the first online store / game launcher that made a real impact on gaming. There was no exclusivity - they were simply the first.
"We are very happy to announce the launch of Darwinia on Steam. Introversion has teamed up with Valve to release Darwinia on their online games distribution platform making it available to millions of new gamers. As part of the launch and Steam's exclusivity, we will no longer be offering Darwinia as a download option from our site, although it will still be possible to purchase shipped boxed copies. At Valve's request we will also be removing the demo from our site for about a month." - Original Nov 15th, 2005 announcement that's still up on Introversions own website.
^ It may have been for a month instead of a year, but for some of the first batch of 3rd party games that came to Steam in 2005, Valve did actually demand that those 3rd party publishers not sell digital versions of their own games anywhere else but Steam (even direct sales on their own website) and on top of that, even take down their own free playable demos from their own websites for a period.