Red Bull had the best car on the grid for this particular weekend, and that's why Vettel won.
Also, you can hardly compare Vettel to Schumacher, in terms of driving ability and style.
Sure, Schumi did win most of his titles in dominant cars (a few of those seasons were a lot closer than most people remember them to be, though), but his performances in not-so-great cars (such as the ones he drove in his first few years with Ferrari, for example) were some of his most impressive.
Vettel, on the other hand, rarely impresses, let alone wins, unless he's in the fastest, most rear-planted (complete opposite of what Schumi seems to prefer, btw) car on the grid, and it just so happens that in the last few years, more often than not, he has in fact been in the fastest, most rear-planted car on the grid.
Vettel just isn't as great a driver as the results suggest, and his insufferable mannerisms just make him look like a bit of a spoilt brat (maybe he's actually a nice guy, but his two default settings of 'cocky asshole' and 'sulky whiner' sure make it seem otherwise). Considering the number of quality drivers on the grid today, he's hardly the most deserving of a title, let alone three consecutive ones.