Do they have long chapters or something?
I don't read very fast at all. Neither do I set a limit - it depends when I'm reading as to how long I read for. I tend to snatch reading where I can - a few pages whilst I'm waiting for my daughter to come out of school, on the park and ride bus if I'm going into town... and I always read before bedtime, but never for a set time/amount of pages.
Some weeks I read loads, then I might have a week where I only manage a few pages!