This episode wasn't for humor, it just happened to involve some of the funnier characters. This was about moving on from the slow and bummer-y first half of the season to the second half, which is almost all good.

Unlike most shows, the LOST writers don't 'sit around deciding what should happen next'. The entire plot has been decided from the get-go, that's why everything that happens is entwined in subtle ways.
Despite what you think, I believe what we've seen here has a definate purpose in the entire series, even if it's just to lighten the mood after several twisted psychological scenes with what happened to Jack, Sawyer and Kate.
Hurley just has that effect I guess - he's the 'fall guy'.
The only thing that bothers me here is that Hurly thinks his curse is broken, but the problem is that he's a Shlameel (Another word is 'jinx'). Bad stuff doesn't happen TO him, bad stuff happens to those AROUND him.
He may be the one with the curse, but honestly the safest place someone could be is inside that van going downhill. I would totally have expected Sawyer and Jin to die by some random thing while Charley and Hurley survive, for that reason.

You can jump start manual transmission vehicles like that you know... not unrealistic at all. It's called push starting.