CS Martin,
Jim Croce is very comparable to Lady Gaga from the Billboard chart standpoint. He had a number of meteoric hit singles in a very short period of time before his death. Lady Gaga has had 6 straight #1 Billboard singles in a very short period of time. Music does not sell in this fashion due to any amount of marketing. When the Beatles had similar early chart success, many said it was due to the way that they were marketed and their haircuts. The fact is, music does not get marketed unless it is good. Record companies have no desire to sink money into people who do not have talent.
That being said, from what I know about Jim Croce, the marketing of himself prior to his chart success was next to zero. He was arguably the least marketed musical superstar in history, which was probably largely a function of his own personality. So just like with everyone else, his music sold because it was good.
How someone is marketed or how they look is totally irrelevant to me. All I care about is the sound of the music. That being said, one guy who was an immense talent, but the sound and production quality of his studio recordings is a bit lacking, is Jimi Hendrix. He is without a doubt one of the greatest rock guitarists of all time, but if you listen to his studio recordings they sound like they were produced by a rank amateur. It is more than a bit amazing to me, although perhaps Hendrix was striving for a "raw", garage type sound. I still consider him to be easily in the top 5 rock guitarists of all time.
Regarding Michael Jackson, I think we all knew even back in the 1980s that this guy was gay and he was certainly an odd and eccentric guy to say the very least, but his live performance at the 1983 Motown TV show was probably the best performance live in the history of television. In the final analysis you cannot fool the consumer, either the music is good or it sucks. If it is good radio stations will play it and people will buy it, it's that simple. Nothing else really matters. Lady Gaga exhibits some of the same qualities of these past artists and I believe her music will hold up over time as theirs did.