I don't think its that big of a gamble for Netflix, they've only just recently started to produce there own stuff (House of Cards, Orange is the New Black, Daredevil) and all of those shows have been met with critical success, I honestly don't know anyone who doesn't have Netflix nowadays, if they pushed Top Gear onto it as well, and put out a big enough ad campaign, they could easily recoup there fee's. There's also the fact that they don't neccessarily have to make a profit on Top Gear, simply having Top Gear only be on Netflix in certain countries will be a big enough to draw to bring in the extra custom.
As for them copy and pasting Top Gear, we'll have to see, but I think its doable.