I think that's the point, it being a lame plot device. It's supposed to sound like something lame that Hollywood movie producers would do (like when they add characters and romance to historical dramas to make them more marketable)- that's why it's funny. It's also funny to imagine Spike and Angel having to sit in a theatre watching Nick Cage!Angel and Keira Knightly!Spike make out and being all uncomfortable and shifty in their chairs. Well, that's what I imagine anyway. I also imagine Spike nearly choking on a JuJuBee when he finds out he's been written as a girl. XD I find it funny at least.