Couple of things I want to point out here:
For everyone who is thinking about using a 1080p output on their ACD 24" may encounter some difficulties. 1080p is 1920x1080, but the ACD's input requirement is 1920x1200. So any bluray player or console typically won't work, unless it has some wonky setting that actually allows you to output 1920x1200. Or if you can find a scaler that will actually scale 1080p to 1200p. These may exist, I haven't really looked.
It sounds like the ACD/iMac's are supposed to get inputs from other apple computers and as such have a wide range of resolution options (aka they didn't put in a more advanced scaler for the input because they assumed the output resolution would just be adjusted via output computer).
As for the 27" iMac's, they are lucky enough to have 720p as an input, which is perfect for gaming consoles. The only difference I want to point out here is that the belfan will actually do HDMI sound (uncompressed 2 channel) over the apple display port. With an HDMI to DVI adapter to the D200, you will need a receiver that will first get the sound.
Most games are 720p anyways, and even if its at 1080p doesn't mean it will look any better. The Matrix game for the original xbox could be played at 1080p, but Zelda on the Wii at 480p looks better. Just because a console can send information to a display for a larger number of pixels doesn't mean the console can actually utilize the extra graphical workspace.
For blurays, you'll have to watch them at 720p as well. Even if the D400 comes out, unless they have a built in scaler that can take 1920x1080 input and scale it to 2560x1440, the dual link DVI will not do any good. You need a source that can output at 1440p or a scaler that can scale a 1080p signal to a 1440p. They are some scalers that will go up to 1080p, but I haven't found any that go to 1440p, it's just not something a scaler would ever care to do (until now perhaps). If you can find one, please post, because that would make the D400 an attractive option for bluray viewing.
Quite honestly, it is likely cheaper to get an external USB bluray player and a copy of windows 7 home premium OEM over a hardware bluray player and the extra cables, converters, and scalers needed to get bluray to work at full resolution.
Long story short:
XBox/Ps3/Bluray playback on an ACD 24" not possible UNLESS you can find a 1920x1080 to 1920x1200 output OR scaler. This is as far as I can tell from reading up on the products without actually owning them.
Xbox/Ps3 on an iMac 27" is perfect, just set to 1280x720 on console (which is the resolution games are rendered at anyways, so no loss in graphical detail)
Bluray 720p on an iMac is fine as well. Does result in a loss of 55% of the graphical detail available on a 1080p signal. This may or may not bother you or be apparent to you.
Bluray 1080p on an iMac 27" same as ACD 24" but needs an even more difficult scaling/output of 1080p to 1440p (more difficult because 1440p is dual link dvi)
Bluray on any iMac can always be achieved with windows vista/7 and an external BD-ROM - playback may not be optimal however:
http://www.cnet.com/8301-18603_1-10381850-73.html