DuracellEnergizer said:

I get that, but it still seems seems odd that Luke would get upset over a simple matter of not being able to buy machine parts right away. If the power converters had been written as a local band Luke wanted to see perform with his friends or something along those lines, it would have been better IMO. As the line is, though, it just comes off as unintentionally funny.

Actually, I thought it came off as incredibly whiny. :) As to why Luke was so whiny about it, the reason comes in the next line: Owen knows that Luke is actually upset about not being able to get away and goof off with his friends. I doubt that Luke actually gave a rip about the power converters, at least beyond them giving him an excuse to see his friends.