I've never seen this before - is it a result of the new rooms added in YHTNTEP? It's always been 3 shops per level - unless using NTTG, which I pretty much never do...
Technically there's nothing hardcoded about shops or zoos. So if you're particularly unlucky then it can happen.
This was the same game in which I didn't find a grinder until DL5 (!) I was doing my vegan "save all the cheese, to grind into omlettes" technique - I had a HUGE stash of cheese by the time I finally found my grinder!
