I respectfully disagree. That might be what students think they are being promised, but it isn't.
That's the irony of BS/MD programs. Students think they are getting something for nothing, but, in reality, schools are pre-screening them. By only taking high stat, highly accomplished HS students, they are stacking the deck in favor of themselves, and are only taking people highly likely, not only to be successful, but to be so successful that they otherwise wouldn't be interested in either the UG or the med school without the program.
Sure, it doesn't always work out this way, and a few people every year end up slacking off and wouldn't be admitted without the guarantee, but they are NOT the majority of people in these programs, regardless of what HS students and their parents think going in.
And no, I'm not saying high stat people don't look at Penn!
I am unfamiliar with dental school admission, but am fairly certain that it is not nearly as competitive as MD admission, so I honestly have no idea what is driving Penn to offer it and not a BS/MD. Come back when Penn offers a BS/MD program and we can talk!!
Edit: Just looking at Penn's website, the BS/DDS is not really a guarantee until after performance is evaluated in junior year, so it's really probably not worth talking about. It looks like the program is nothing more than a tool used to recruit awesome applicants away from schools like Harvard and Princeton, with no real guarantee attached.
I personally know someone, whose dad is a dentist who with a Penn dental degree, who could afford to go anywhere, who turned down Penn dental to go to Rutgers, so I'm just not sure how amazing its reputation is, or what going to a top school means in the dental world, so I just don't know what a dental school guarantee means for anyone good enough the accepted to Penn UG. FWIW, USNWR doesn't even bother ranking dental schools, so there's that!
Apples and oranges compared to something like the BU program, which is designed to pull high stat applicants who would never otherwise consider BU from schools like Penn. While BU is a very fine school, it is far from elite, both UG and med school, unless "elite" means T50 in Boston.