Americans, Japanese, Belgians, Indians and Eskimos also don't do diacetyl rests so long as they pitch the correct amount of yeast and ferment properly. However, with some strains a diacetyl rest is still recommended. See below from the Wyeast website:
"YEAST STRAIN: 2206 | Bavarian Lager
Used by many German breweries to produce rich, full-bodied, malty beers, this strain is a good choice for bocks and dopplebocks. A thorough diacetyl rest is recommended after fermentation is complete."
I believe Wyeast and Whitelabs put these kinds of statements in their descriptions because their expecting people to under pitch and stress the yeast. When the yeast become stressed, they will throw off more diacetyl, amongst other compounds. By letting it warm up that can help the yeast clean up it's own mess.
As long as you're pitching the right amount of yeast, you may not need a diacetyl rest.
SO, I ended up doing a D-Rest for 4 days per the Wyeast recommendation for 2206 and the activity picked up dramatically. At the start of the D-Rest it was at 1.013 and I kegged it last night at 1.012. So it dropped a point but that does not seem like a lot for 4 days of activity. So what was the activity then? Tom mentioned CO2 release by diacetyl reduction not being part of the pathway. So what was happening? As previously stated I thought it was due to the yeast cleaning up the beer but now I'm thoroughly confused.....
Sorry to hijack the thread, but it still seems to fit with the OP and subsequent replies.
Since you're moving from lager fermentation temps to pretty much room temp, there would be much more CO2 released than what you would see with ales. Colder liquids absorb CO2 much better than warmer liquids. I'm betting this is what you saw.