I don't know, is it really a "catch"? Why would you not expect it to be this way?
Where I think it makes sense would be for someone who wants three or four plugins that aren't in the same bundle(s). Rather than buying two or three bundles or paying full price for each individual plugin on the Waves website, you configure your own bundle and you're good.
Where I'd imagine it wouldn't make sense would be for someone looking at the Platinum bundle who decides to switch out half of the plugins in the bundle for different ones. Then I think it would be reasonable for that custom package to be more than the standard bundle.
I guess it remains to be seen what the real details are...