Ultimately I think this is an outcome of asymmetric price elasticity: People who are downstream limited tend to be on the consumer side. Even if they might be

Ultimately I think this is an outcome of asymmetric price elasticity: People who are downstream limited tend to be on the consumer side. Even if they might be willing to pay more for higher bandwidth it's more a convenience than something they really need. So in order to actually get them on a more expensive tier, the ISP has to offer an upgrade with a relatively high bandwidth per dollar difference in downstream. People who are limited primarily by upstream however tend to be be more of the productive side and, if what they have is not enough, there is probably some form of urgency for more. They will jump on higher tiers for much smaller upstream deltas than their downstream-limited counterparts. I don't know if there is an actual technological or logistical reason forcing ISPs to only offer one up/down ratio per price tier, but if they offered selectable asymmetry or symmetric, they would either get less money from downstream users (not attractive enough to upgrade) or from upstream users (problem solved at a lower tier).