I programmed a sportbook system. I can tell you that, as a programmer, I was completely in favor of timeouts. I thought the timeouts should be approximately 10 minutes (though on request I had extended it to 15 or 20 in some cases).
This system was WEB/HTML based (not a downloaded program). For a web system, unless the player logs outs, the book has NO way to know if the player has finished or shut off his computer. 10 minutes of idle time is pretty standard for most applications to assume the user has walked away.
And, yes, it is a deterent to the wiseguys picking you off. The design of online system is modeled on this chain of events:
1) Player logs in
2) Player checks lines
3) Player bets everything he likes
4) Player either logs off or refreshes the screen if he is interested in making more bets.
A player hanging around to catch a DonBest line move and bet it with in the 5-10 seconds it may take a clerk to notice the same move is NOT a design feature that anyone purposely creates for a sportsbook. Either the player is actively engaged in surfing the site and checking lines, or the player is considered logged out.
That said, we did have a one-button quick relogin feature to make a timeout less painful.
It is MY position that timeouts longer that 10 minutes don't help the book and are not a hinderance to normal play.
If you were logged into a casino instead of a sportsbook, 10-minutes of idle time would be a strong indication to the computer you are done.