I guess it's because we aren't used to thinking about a guitar as something "disposable" - I mean, I fully accept that my laptop will become "obsolete" (okay, it will still be able to be used and still function, but it will probably need to be upgraded at some point) in about 5 years - that is just the lifecycle of that device - the Variax is kind of the same way, I guess. At least with the magnetic pickups, they can still function as an instrument for the rest of your life, really, even if the modeling hardware no longer functions. The old Variaxes didn't have that going for them, although I suppose they could be retrofitted for pickups or as 13 pin Roland GK / piezo system guitars with a change of electronics. As long as Line 6 continues to use piezo bridges and there is a decent sized electronics cavity in the body, you could still make use of the guitar - and updated boards MIGHT be able to be retrofitted into the cavity, depending on if Line 6 offers those kinds of materials to their authorized dealer/repair shops or if you can find "donor" instruments.
Bottom line is I guess you just have to enjoy the guitars for what they are and get your joy and use out of them, like someone else said about keyboards. :-)