One thing I noticed by eyeball during the trip to Amsterdam was that there seemed to be many fewer coffee shops in town than I'd remembered from ten years ago. According to Dutch political sources, this is actually the case. The change stems from two things, one being that they made it much more difficult for institutions licensed to sell marijuana to also sell beer (thus wrecking the business model, though I should note that I did see a whole bunch of people smoking weed they'd presumably bought elsewhere in one bar) and the other being a simple change toward a giving out fewer licenses.
The political reason for the change is the rise of the smallish Christian Union Party, which combines some egalitarian ideas on economics with cultural conservatism. Cultural conservatism by Dutch standards is pretty mild by American standards -- they pushed for it to be the case that civil servants with objections to gay marriage can be allowed to refuse to perform them personally; actually getting rid of gay marriage is unthinkable -- but apparently includes some skepticism about tolerance of soft drugs. The policy reason is that the soft drugs for sale in the Netherlands had been getting stronger-and-stronger leading to a lot of problems with "drug tourists" unaccustomed to the Dutch product finding themselves in various kinds of trouble.
This seems like a sensible enough concern to me. The legitimate concern about marijuana legalization, in my view, is that the creation of a big marijuana industry could have some real deleterious effects, which I guess is what you were seeing in embryonic form with competition leading to an increasingly intense product. The Dutch policy has been aimed at the sensible goal of preventing the emergence of such an industry -- no advertising, no large scale cultivation, etc. -- while still letting consumers do what they want in private, and some cutback in the number of coffee shops in central Amsterdam (it's still no hard to find one) seems consistent with that.
Matthew Yglesias is a former writer and editor at The Atlantic.