Yeah there's a pretty big difference between limiting yourself to 280 characters, and limiting yourself to 40 pages. Limiting yourself is great. Handicapping yourself is bad. I find the character limit in Twitter also contributes to society's increasingly poor grammar, as well.
However, there are cases where there isn't enough space to articulate an idea. In those instances, I've tended to not Tweet at all.
Twitter is just a poor tool for communication of nontrivial ideas.