No particular wallet in mind.
I was under the impression wallet address's are limited to 100
One might be ..... but they are all just software programs ... each one can do what its programmer wants.
Or maybe one has 100 addresses as "default"?
100 addresses and private keys are generated upon initial startup of the reference client (Bitcoin-QT).
So, if you backup your wallet immediately after startup, it will have the first 100 addresses that were automatically generated.
After the first 100 addresses are used, new addresses are created, but won't be a part of the first backup.
This is why it is important to back up your wallet often if you use Bitcoin-QT.
But there is, to my knowledge, a hard limit to the amount of addresses that can be generated and stored in a wallet.