, yes sir, I know, I use Libsyn. I'm a fan. ;)
As +Angelo Mandato
mentioned, it's a lot more difficult to scale web servers to accommodate a lot of traffic, which makes "unlimited" a fantasy.
On a (kind of) unrelated note, back in 1995/96 the hosting company I worked for ran 20 unix and Windows servers...out of our office...on a T1 line. But that was common practice back then when sites were nothing but small static files and images. We didn't even have a stated bandwidth quota, because bandwidth was a non-issue where the typical site was concerned.
This should give you some idea of how different it was then: we had two plans, a 25MB and 50MB, and we charged $25 and $50 per month for them respectively. Imagine that. And we had 25,000 customers. You can do the math, but suffice it to say hosting was a much more profitable business in those days than it is today. In the past 7 or 8 years there's been a real "race to the bottom" in web hosting (and a consolidation of companies by one particular investment firm), and the lower level of quality at the majority of hosts now is the direct result of that.