Pelvic exams have nothing to do with bringing on labor - believe me, if they did you would see 98% of mom's in the Dr's office daily from about week 35 on! :)
It all depends on the doctor, nurse, or midwife (some feel better "regularly reviewing the situation" and some take the "It is gonna happen either way so who cares" tact).
I had the same question with my first as to why I wasn't getting pelvic exams. The midwife had a great explanation for me which made sense. First, she asked if I wanted one because she would be more than happy if I felt I wanted or needed it. I said "Well, how can you tell when or what is going on and when I will deliver if you don't check?" She explained that whether I am 0 or 7 cm dilated, effaced or not...it really has no way of directing when I will give birth. She said it happens when it is supposed to, and not to worry. It could be an hour from then or two weeks from then, with or without knowing dilation and effacement - checking wouldn't change a thing or predict any sort of reliable result. I was a bit skeptical of this answer until my mom explained my aunt was dilated to 7 for 5 weeks before she gave birth to my cousin. I was under the misguided perception that moments after effacing they pretty much just popped right out (yeah, right)!
In talking to many people I have heard these stories. So, if you feel more comfortable with having one done...go ahead it will not hurt, harm, or have any sort of bearing on when or how you will give birth.