It might be $50, but it also contains less content/problem sets. Some of the cheap books published in countries like India have as little as 15-20% of the content than the same US edition contains.
This will only hurt those countries. Publishers will just stop producing International editions and you will have the same, high priced edition, world-wide..which will price many of those people out of the market completely.
Even if we assume that publishers stop producing separate International editions, there is no reason to assume they will price them identically in all regions. More likely, they will price them in a way that they think will maximize their profits. If this price is judged by the international audience to be too high, the market will respond with increased piracy. Eventually, some other publishers will enter the market with a reincarnation of the "International edition" lured by the siren song of potential profit.
In the alternative (http://en.wikipedia.org/wiki/Alternative_pleading), if the International editions truly contain less content than the standard edition (15-20% of the content), and hence less value, perhaps the international price is simply fair value here in the US as well? And if so, why should sale at this price (plus profit for the importer) be prohibited? I find it more likely that the captive nature of the US audience (required textbook of a specified edition) allows the US edition to be priced at a premium beyond that which the information content itself would justify.
While I'm not saying this might be true for every book out there, but I completed most of my bachelor's and my master's engineering degree by buying low priced edition from India and SE Asia and I used to verify and compare with US editions and never once did I find any major differences in context or additional problem sets.
The quality of paper wasn't as good, but the price difference was huge and well worth the effort for me to be able to afford them.