The difference is one of those shows eventually found its footing (making its premature cancellation that much more cruel!
Any series' that takes 3-4 seasons to "find its footing" has been on way too long, and, by definition, couldn't be "cancelled prematurely." I am no fan of shows getting axed after 1 or 2 episodes, BUT if a series' can't find itself or an audience in 1 or 2 seasons then it needs to go.
Personally, I gave "Enterprise" a season and a half before I stopped watching. Now, I heard from many folks that it started to right itself in its fourth season, but so what? No one can say that ST: ENT wasn't give a fair shot.
The problem, pure and simple, was everyone took Star Trek for granted. They ALL figured if they put something, anything, out there that was set in the Trekverse that all the "trekkies" would go for it in a big way. Even the actors spoke of there association with Enterprise as a windfall which would bring them financial independence.
What surprised them was that the slim majority of Trekkers were discerning and had standards causing them to quickly turn their backs on the lackluster effort known as Enterprise. Sadly, however, there are more than few die-hard fanatics who would watch a dog taking a dump in a forrest every week if you labelled it "Star Trek." The slow leeching Braga & Berman started with Voyager turned into a full blown hemorrhage with Enterprise. And when it was diagnosed as terminal B&B just shrugged their shoulders and walked away. Poor Manny Cotto was left to make the funeral arrangements.