"Top tier" is a designation related to research funding. If one doesn't want to be a biomedical researcher in a powerhouse academic position, then any other med school in the country will do, because they all teach the same material and provide you with the same privileges following graduation. This has actually been discussed quite a bit.
If a doc is all you want to be, any state or private MD or DO school will get you where you want to be.
This is not entirely true.
Your first two years (sometimes 1.5 years) of medical school are classroom based learning. It is very similar at most schools with slight modifications about how much PBL or other 'types' of learning the school integrates in the place of some lecture. The quality of the education is seen as relatively similar because the curriculum are relatively similar. They all teach at least a little bit toward Step 1, which you take after your second year. Other than helping you prepare for Step 1 and laying the framework for everything after, your first two years of medical school are largely irrelevant for residency and beyond.
Third and fourth year are clerkship based or in other words clinical. The quality of education varies significantly. Take a gander at the allopathic forum. People complain left and right about poor rotations, bad preceptors, lack of resources etc. While a 'top' school is not immune from those things, the education is different at different schools. And yes, it does matter. The starting quality of interns is a reflection of who they are, first and foremost, but also what they have done their last two years in medical school. It is astonishing the number that show up and an H&P is difficult or organizing several patients is difficult. These are skills that take time and practice to develop. If a school doesn't set reasonable expectations and have the infrastructure or culture to push students along, they don't develop. This makes for people that are just terrible coming out of medical school.
Yes, you will be a doctor coming out of any MD or DO school, but do not kid yourself. I am one of the largest proponents on this forum about no matter where you go to school (MD) you can end up in just about any residency. But, it does matter to a certain extent, not just for the reasons above. A lot of residency matching in the more competitive fields or at more competitive institutions is about networking. We call the letter writers of every single applicant we are seriously interested in. Granted we are in a smaller specialty and can do something like that, but who people know matters and coming out of a powerhouse is going to do you favors down the road. Couple that with the fact that many schools are feeders for certain residencies (think HMS feeding MGH, B&W, BID), there are very good reasons to want to go to the 'best school' that you can.
All of this having been said, most pre-meds have no idea what "top school" means and the concept of a "dream school" is a little silly. The vast majority of those people are being driven by parents, ego, misinformation etc.
