Turkey doesn't have Iraq's potential for generating revenue. Turkey also associates itself more with Europe hence it's bid to get into the EU. Turkey isn't really embraced by the Arab world, they're considered their own thing.
Turkey also hasn't got the exposure that Iraq has. And yes, Iraq will be a successfull democracy. We did it with Japan, we can do it with Iraq. America is actually pretty good at nation building. We do carry some selfish motives, but, unlike the countries pushing for UN control, we don't steal. We're not going to put things in place that only allow us to benefit at the expense of the Iraqi people. The Iraqi people will be the biggest winners in the end.