The video limits are mostly explained on page 151 of the User Manual.
There are several reasons/times, not just one:
Capacity of the Memory Card.
Size of the image being used (HD video is the shortest (about 11 minutes).
Size of the maximum file size (limitation of the file system system) 4 gig).
Temperature of the camera.
European Union Tax Law (29 min, 59 sec).
A videographer should choose a camcorder if they are doing serious video shooting.
Canon sells still-cameras and camcorders and is not likely to sell a camera that does both equally well.
That would impact sales on one (or the other).
..
I'm told that the Canon T3i, and similar, cameras can only shoot for around 15 minute intervals and needs to be turned back on or reset?
Seems like a real deal breaker for most videographers.
Did I get bad info?
I am amazed that that fact is no place to be found under the reviews or comparisons.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic