Is that true?
I'm not using mine as my primary router, but my network is made up of multiple Airport Extremes.
I honestly don't know. I spoke to several Apple senior support people (I can't remember their exact job title) throughout the course of ~2 weeks.
The first person I spoke to had me set up my Time Capsule in bridge mode and said that I would have no problems at all. This person also told me that Apple doesn't like its support people assisting customers in setting up a Time Capsule in bridge mode. Apparently, they're supposed to say that it can't be done (which one support person actually told me a long time ago). That support case was closed.
The second person I spoke to stated that I might run into some difficulty down the road with my Time Capsule set up in bridge mode (my call had to do with a different issue about the Time Capsule). That support case was closed.
The third person I spoke to told me that corrupt backups were pretty much guaranteed to happen as some point in time. She said that the Time Capsule was designed to be used as the primary router or not at all (even though it can be set up in bridge mode). She was adamant about it, and assisted me in changing my Time Capsule to my primary router. She was also a bit rude. That support case was closed.
So yeah. I really have no idea. But right now my Time Capsule is my primary router (even though I don't want it to be). I can say that during the short time I had my Time Capsule in bridge mode, I didn't have any problems with my backups. I never did a full recovery from my backups, but I did recover a folder without any fuss or problems.
EDIT: If someone can tell me on good authority that using Time Machine with a Time Capsule in bridge mode won't present any complications as compared to using it with a Time Capsule as my primary router, then I will definitely consider buying a new Time Capsule. A better solution would be one that doesn't require me to purchase a combo router/drive. I would prefer buying a backup drive that can be used reliably with Time Machine and a third party router.