Think the minimum odds was probably more relevant under the old rules of including your 1pt stake in the returns. Under those rules, people could've backed 5 teams at 1.2, and as your returns are doubled for 5 winners, they'd be scoring 12pts. Under the new rules they'd only score 2pts for that, and as you say, they're not going to get far with that.
As for the maximum odds, 10 or 15pts is a pretty big margin in the context of this competition (more so under the new scoring rules). For most of the competition, I'd agree with you that if you want to back QPR to win at Stamford Bridge, fair play to you. In the final weeks, though, I'd say allowing big odds like that leaves it open to people adopting a bit of a scattergun approach, backing 5 teams at big prices and hoping that they get lucky.