Hey peeps,
I sell (or attempt to sell
) a couple of pieces of software on Handango, PocketGear, and Clickgamer. Don't detrimentally rely on this or anything, but I'm pretty sure that if you read the agreements closely, you'll see that each distributor requires only that if you make a demo version of the game available, you direct the user to purchase the software at the place where they got the demo version.
So, for example, with Quest of the Styli (the game I just released) I have two versions of the software. They are identical to each other except that one of them, when it starts and exits, says "purchase the full version at Handango" and the other says "purchase the full version at Clickgamer."
Also, note that if you don't have a demo available, none of this applies (i.e., you don't have to mention that you got the full version at whatever site). As a side note, I've become disenchanted with PocketGear and so am no longer going to distribute my stuff through them.
Hope this helps!