Yes, there is indeed a limit. At the Chanel boutiques, it's one bag a month (no matter if it's classic or not), and I forget how many small leather goods a month (2?), as well as limits to the number of classics you can buy. The limits are higher at NM stores but they also have a limit. Interestingly enough, they don't limit you on RTW or fine jewelry (except watches) or exotic bags, at least currently.
The reason? Ostensibly to prevent resellers, but then some SA's are working hand in glove with resellers, so the true reason is to create an illusion of scarcity or some such malarkey. That makes the bags more illusive and therefore more desirable in the minds of corporate types. It's quite silly.