I wasn't implying anything; I said it outright. And jamcat probably explained it better than I did. Getting an A in a course will show you are top of your class. When that class is filled with higher quality students (again, your words, not mine), then it gives the adcoms a better idea of where you stand. Sure, you might be extremely bright and get an A in Biology wherever you go. But the adcoms get a better idea of what that "A" means if it comes from a program they know better. And they tend to know the 4-year colleges better than the CC's.
I can't speak for CC's and any experience I present will be incidental, but I'll throw it out there anyway and you can take it how you will. I had 4.0 sGPA when I applied to med school. Even though I did well at Harvard Extension, I found it challenging and my midterm/final exam grades fluctuated. When I moved back home and took Biochem during my lag year at a city college (not a CC, but a 4-year college in the city not known for their science focus), I was literally top of the class. Great for my ego at the time, but I don't realistically believe I would have been top of the class if I took Biochem at Harvard Extension. So, yes, I do believe there is a difference in the quality/difficulty of education depending on the institution. My Biochem course skipped the Pentose Phosphate Pathway (HMP shunt), which I thought was surprising.
As for your second question, yes, I do believe getting good grades at Harvard Extension helped a lot for getting interviews. It's a program that regularly churns out medical school applicants and adcoms are familiar with it. I also got a committee letter from the school. I have no clue what it said, but I received interviews at some research-centric schools despite my weak research experience. Would it have been any different if I chose to go the CC route? Who knows. But I feel the grades and letter from an established program probably played a role.
Don't get me wrong. I'm not trying to bash CC's. It's great that a lot more med schools are accepting their courses. But if someone is browsing these forums looking for advice on whether to go the CC-route, my honest answer is that it sounds like it may affect your chances. Whether you choose to risk that is up to you. I was only giving myself one shot at this, so I didn't want to risk it.