There are only two reasons why it wouldn't be funny -
1)The viewer cannot relate, because they aren't familiar with the "world of otaku" enough to appreciate the inside humor.
2)The viewer IS an otaku, or uncomfortably close to one, so the defensive mechanism kicks in to either belittle the parody or just find it unfunny.
Personally I find it funny except for the bits that I go "hey....um, that's me."
Odd. I found the "Hey, that's me" bits to be the best parts.