"They" never fail to come up with more things to be worried about, do they? After my first child I was told not to drive for 6 weeks, on top of no baths, no this no that...etc. (and this was not in the 50"s-she was born in 2004)
Although, "they" have valid concerns for protecting pregnant/post pregnancy women, most advice is based on "worst-case" scenario. For instance-6 years ago it was OK to eat hot dogs and deli lunch meats-now a lot of OBGYNs are against it because to the remote possibility of ingesting harmful bacteria. (They do realize, of course, that the body is exposed to harmful bacteria, on a daily basis-don't they?)
Don't get me wrong-some advice is great, important and has saved thousands of lives, but, I think a lot of medical advice is overkill.
Yes, worst-case scenario, you could get an infection, but the likelihood, especially if you keep your tub clean is very very very slim- so tell your OB to go soak and you do the same.