It would be great if a band left the stage for this purpose and everyone stayed quiet instead of applauding like seals barking for a fish they know is coming...
"Oh....you WOULDN'T LET US LEAVE!"
"Shut up! You wouldn't turn on the lights!"
The obvious reason for the encore break is so the band can start prepping the post-show inbibing so they peak at the right time. It takes a few minutes to get buzzed.....about the time it takes to do A.) a fan favorite and B.) their biggest hit which a band can usually do completely f'ed up.
Suede did that "Let's pretend we didn't go off for five minutes. Here's the songs we'd do for our 'encore'" a while back at WUST, didn't they?
Also, when they were dewy-faced, most-hyped-bands-on-the-planet, The Strokes and Oasis didn't do encores. Mainly due to the fact that they probably didn't have enough songs to.
Brian