It's difficult to compare these two as their design and approach is totally different (one being rack mountable with voice-modelling capabilities and the other a foot controlled creature.
Naturally with the VoiceLive 2 being a newer product, it does indeed benefit from higher quality/most up to date technology effects and great new features - although again, approached in a totally different way to the VoiceWorks Plus.
For a more in depth understanding of how the two units differ, I'd suggest trying them out at a store near you and even having a read through the manuals (downloadable for free via the TC-Helicon website).
It's also worth noting that the VoiceLive 2 is a product we are constantly updating via software updates which provide ongoing improvements, new features and bug fixes.
To answer your questions:-
Is the reverb updated/better? Yes
Is the pitch correction algorithm updated/better? Yes
Has the mic pre section been updated/better? Yes
Are the presets the same? No
Hope that helps!