I've never heard this rule that you should only grocery shop once every week or two. I don't see why that would be a rule!
Like Villanelle I prefer / need to shop twice a week or so. For one, I'm on foot, so can't carry enough food to last a week for two people. And secondly I don't meal plan that far in advance! Thirdly, I eat mostly fresh foods, many of which only last a week or so.
When you grocery shop on foot you have different requirements, I guess. I also don't go to one store (I don't remember the last time I was at a supermarket), but rather three or four small stores... One for produce, one for cheese, one for meats, and a health food store for bulk things (rice, nuts, etc) and pretty much everything else. And a farmers market, which is also a 10 minute walk and has a little bit of everything. So food shopping is a very pleasant experience... Why not do it as often as possible? (While only buying what's needed, of course.)