It has nothing to do with the technology at all. A cable modem has perfectly adequate performance for a lot of commercial uses and the telecommunications companies want those customers to have to pay 50X as much for a leased line.
Which is why it doesn't make any sense for Google to be doing it. Their purpose isn't to upsell business customers, it's to demonstrate demand for high bandwidth connections so they can pressure other telecommunications companies to increase capacity.
The whole "heavy users" thing is bunkum. Yes, 20% of the users transfer 80% of the data. That's how pretty much everything works. People are diverse and have non-uniform usage patterns, and if you sort by consumption level then the high end tautologically uses more per capita than the low end. But bandwidth is by far not the predominant cost of providing internet service. The predominant cost is getting the wire to the endpoint whatsoever, once it's there you can send as many bits as you can fit and upgrades are a matter of replacing terminating equipment rather than going back into manholes and bucket trucks. If bandwidth consumption were to quintuple it wouldn't require any significant rate increase -- it has been increasing exponentially for years with no real trouble.
The only reason telcos talk about heavy users is that they want to engage in price discrimination and they know it confuses people who are used to dealing with commodities whose dominant cost is the unit cost rather than ones whose dominant cost is the fixed cost of building a distribution system.