First of all I think it is a very, very bad idea setting up a catchall forward address!
I think not offering this feature is a good way to prevent people using it
If you set up a catchall forward address, all the mails will be treated as coming from your server. So if someone sends a lot of spam to that address and you forward this to - let's say - googlemail, your server will be blocked sooner or later due to spamming! CBL listing would be a matter of time, too.
ISPC3 is indeed a completely different software. None of the codes of ISPC2 was used, it was written from scratch.
It uses a lot of different techniques to achieve the features.
Would you talk of Confixx and Plesk being the same software in different versions only because they offer similar features?