The line 6 devices simply does not give a good sound. I don't think anyone is really saying that in terms of modulation or delay effects there is anything missing from reason, but when it comes to tone, and specifically getting a good one from a quality guitar, you just don't get it through these devices. I ended up buying an Orange Tiny Terror and an SM57 to get the sound I want.
If I'm honest I've only ever found Amp Designer in logic to be any real use for guitar amps, I've also had Guitar Rig and AMplitube in my time and they just didn't cut it. I think the OP makes a valid point, all these REs and nothing for guitarists. It's a pity, Reason is almost the ideal environment for the guitarist with the SSL evoking older mixing desks and classic techniques. I might have stuck with it as my main DAW just for it's ease of use had I not gone elsewhere for MIDI and a few other features.