Although your point on efficiency stands (at least with data structures that have to reshuffle contents on deletion), the type of loop that you use has nothing to do with the order that you delete the elements. You could easily do something like:
while (MyControl.TabPages.Count > 0) {
MyControl.TabPages.RemoveAt(MyControl.TabPages.Count-1);
}
For loop are nothing more than while loops with:
(1) an assignment (int i = MyControl.TabPages.Count in this case)
(2) an extra command (i-- in this case) added to the end
Sure. Though if we're talking about efficiency, I would imagine that counting backwards would be slightly faster than getting the current count each time. Though in reality this depends on way too many factors - I imagine TabPages would be stored in cache and getting the count is just as fast as counting backwards. Micro-optimization and all that.
Regarding for vs while, I find the choice is important only in the intent they emphasize: while puts emphasis on the condition, whereas for puts the emphasis on the iteration. I think in this case the condition (that the list is not empty) is deserves more emphasis than the iteration through the elements of said list - hence why I find the while version to be more readable. YMMV and all that :)
Exactly. For example in JavaScript doing a something.length would result in re-counting the number of elements, while doing the loop in this style would efficiently store the count in a variable that is fast to access and manipulate. I suppose if you want to be a real optimization junky you'd also use --i instead of i--.