Plasma/LCD wall mount - what stops you using it for a bigger tv?

[Juzzie Wuzzie]

Let's say you have a 30-37" plasma/LCD wallmount. What stops you using it for say a 40/42" television? Assume that it is well bolted to the wall, so weight is not going to be an issue.

 

[Andrew Everard]

Basically whether the mount itself is strong enough to hold the TV, and whether the fixing points are adjustable enough to accommodate the greater size