I signed up for GameTap today, so I could play Sam & Max. The GameTap interface does support 1440x900, 1680x1050 and 1920x1080 (among some other lower WS resolutions), but Sam & Max does not.
It only supports 4:3 - 1024x768, 1280x960 (notice not 1280x1024) and 1600x1200. Great game, and enjoying it in Pillarbox.
TellTale Games has a forum that some of their staff and developers post to. I posted a lengthy (but very polite) thread about widescreen and asking why they don't support it. You can see it
here. This is one of the few developers that I've seen with active people on their forums, so hopefully it will be a chance for us to hear back as to why someone wouldn't support widescreen.