*IF* the purchase price went toward the full game. If I purchased a $10-15 "demo" I would probably feel cheated by purchasing the retail version at full cost otherwise.

Actually, World of Warcraft limits what data is sent to you by distance, rather than an entire instance or "zone" etc. In EverQuest 1 they originally sent all of the data for the entire zone (to get an idea of size, some zones would take more than 10 minutes or more to cross), which led players to develop tools like ShowEQ and MacroQuest, which would obtain the information for everyone else in the zone and display it to the user. If you were looking for something rare to kill for the phat lewts, you didn't need to be anywhere near it. So, besides the obvious bandwidth optimizations from limiting to a smaller area, games that intend to sell well will typically limit the distribution of information in order to help prevent various types of cheating.