I am a professor at a local community/tech college and teach and advise dual enrollment students all of the time! The discussion on AS/AA credit versus AP exams comes up fairly often, and my students (who've clearly opted for the college credit) say they did so because of two reasons:
1) The materials are laid out and tested along and along during the class and not all at once like the AP exams are. I absolutely see their point here: I took AP exams while in high school, and the pressure to do well on that one test was insane.
2) AP exams aren't a true model of what college looks like. Yes, the AP exams do cover advanced material, but the structure of the AP class leading up to the exam isn't what we do in a typical intro class in college. The dual enrollment students are thrown into a college environment where they have to sink or swim alongside traditional college students: my high school students are always intimidated by being in that classroom for the first week or so, but they are challenged by being around older students. Nearly all of them rise to the occasion!
In my advising experience, high school students who apply themselves in the dual enrollment program are incredibly prepared to transfer to any of the 4 year colleges in our state. In fact, the faculty advisors are constantly tutored on what the 4 year colleges are looking for from our transfer students, and the 4 year colleges are quite open with us on what they need.
I know it varies from state to state and institution to institution, but my CC (which is the largest in our state) routinely sends students to our local 4-year universities, many times allowing them to transfer after a single year. (I recognize that we may be a specialized case since we do work so closely with other colleges/universities in our state, and that other CCs may require the full 2 years to be completed before transferring).
In any case, please let me know if you have any questions about the dual enrollment program or how it looks to 4 year colleges. I'm happy to help!