I just spoke to Jeff, here's the skinny:

Line6 Variaxe Guitar:
- Does pickup and guitar modeling only.
- Does not do alternate tunings.
- Allows you to duplicate the sounds of many popular guitars by using its selector switch and knob.
- Not programmable, choose only from its built-in presets.
- Form factor: Actual guitar.

Line6 modeling Amplifer:
- Counterpart to the Variaxe, does amplifier modeling only.
- I think it has some built-in effects.
- Form factor: Actual amplifer/speaker cab combo.

Roland V-guitar system:
- Does both amplifier and guitar modeling.
- Includes built-in effects as well.
- Programmable, can create your own presets by modifying parameters and saving them.
- Does alternate tunings and unusual instruments.
- Form factor: Floor pedalboard, can add it to any guitar by attaching the hexaphonic pickup.
- Works best when plugged directly into a mixer (so that your amplifier doesn't color its amp-modeling sounds).

So there you have it.