Konradical: http://www.gametap.com/video-games/Psychonauts-20000336-13.html
This game is, and has been a free download on GameTap for a very long time now. It's actually how I played it for the first time, and promptly removed the service :p.
So... Why GOG? If they were aware of the alternative, few people would dish out 10$ to get the game here. In fact, it doesn't seem like good business sense to try and sell a product which is available for free elsewhere. I love both the game, and GOG, but I'm wondering if anybody but the hardcore GOG fanatics who "must have every title" will really buy this.

Namur: Gametap is a 'download to play' service...
You should really look into what services like Gametap or Metaboli are about before making this kind of posts...

Namur: A 'download to play' service gives you acess to x number of games while you have an active subscription to the service. If you cancell/give up on that subscription, you won't have acess to any games at all. So, while you can play the games in the 'package' you've subscribed to provided you have a valid subscripttion to the service, the games are never yours.
If you buy the game on gog or someplace else, the game is yours, period.

ruckboos: Ah, so Gametap could theoretically remove it from their Free package or whatever. Gotcha.
Then I'm glad I paid for it!

VirtualPenguin: Also it's more than worth the money! I happily paid 3 times the price for the disc, and would happily buy it on gog if there were more extras

Namur: Indeed they could.

figmentPez: And they have, several times in the past if I'm not mistaken. Psychonauts, as with other games, goes on and off the free games list on a regular basis. I think I played Psychonauts for free on Gametap, but it might have been after I subscribed. Whatever game(s) I played for free, I had to watch a commercial before playing each time, until I ponied up $60 a year for a paid membership.
Even with a paid subscription, there are drawbacks to playing Psychonauts on Gametap, all of them related to the encryption Gametap uses on all it's games (part of it's nature as an "all you can eat" service).
1. As Namur already mentioned, you have to be online to play.
2. No 64-bit OS support for Psychonauts and most other Windows games. The old encryption driver Gametap is in a process of switching away from only supports 32-bit versions of Windows. Each game has to be re-encoded and playtested to switch over to the new process, and less than 2 dozen games have made it so far.
3. No way to use Linux. I'm not sure how well Psychonauts runs under WINE, but even for games that do, you can't use Gametap to do so.
4. No way to backup or transfer saved game files. The entire installation folder of Gametap is encrypted (at least under the old system), and to the best of my knowledge that's where Psychonauts stores it's saves. So, if you need to reinstall or swtich to a new computer, your game progress can't go with you. (This isn't a problem for games that save to My Documents or other folders, but a lot of older games saved in their own directories.)

Petrell: Modding games is also impossible so no widescreen/highresolution mods, no community fixes, no content restoration projects etc.