Using the US as an example, bandwidth costs from major Tier1 providers will range from around $0.75 per Mbps (Cogent) to $5.00 per Mbps (someone like Internal). The theoretical throughput of 1Mbps fully sustained is 324GB per calendar month. You can see from the maths that the law of averages does kick in and some overselling will exist, even when using lower-quality, cheaper bandwidth providers.
So I'm back to where I came in - are they simply misleading, and not expecting many to reach such high throughput and therefore likely to pull anyone who gets high throughput (which, with streaming audio will be probable)? Or are they genuinely differentiating themselves and taking slim margins? Of course, some are happily selling (and buying) domains at $35 compared to the more-usual $8-12.