Having the same fee for transferring both 1 USD and 10,000 USD is absurd - it is obvious that for the user these two transfers have extremely different levels of usefulness.
Saying it's absurd is a bit strong, don't you think?
It costs the network no more to transfer 1 BTS than it does 1,000,000 and that holds true for all assets.
However, the price of an item is not only related to what it costs to produce it. It raises the issue of what profit margin is reasonable, or better stated, what profit margin can be obtained from the market. It's a matter of demand, and right now demand is low on all fronts of this ecosystem.
In general I think there is merit in a 2 tiered approach as you describe here, and basing it on the asset itself rather than in terms of the equivalent BTS value is an excellent way to simplify the determination of which fee rate the transaction falls within.
This same approach might also work for other assets transfers, but b/c of how UIAs are created the approach isn't necessarily as clean. Even if it was allowed for UIAs, even to the extent of allowing the threshhold to be set by the UIA creator, the effort required to implement it may not be worth the benefit to the ecosystem. For bitAssets no GUI effort is required. The threshhold value could be just another set of parameters set by the committee.
I thinks it's best to try this out on bitAssets first before implementing it elsewhere.