If they bought software for a single purpose (or a set of purposes) and that purpose hasn't changed since years ago, why should they be forced to upgrade?
If the software is potentially connected to the Internet, then it represents a security risk which becomes greater the longer people have to learn about it its bugs. If it is not maintained, the case is even stronger.
People should have an up-to-date, high quality browser for Internet use. People should not have two browsers, because they will confuse them.
You maintain or replace your car. The same is true for internet-capable software: the Internet is continually evolving and you need to respond to that.
Comparison with cars is a valid one, although maintaining it is much easier than upgrading the software; moreover, you can fully enjoy current road network with a 1960 car.
I don't buy the rest of arguments. "People should have an up-to-date browser"... why? By that reasoning, you should forbid the existence of elinks and friends. I'm pretty satisfied with my current web experience (which, for me, hasn't changed much during the last decade) why should I be forced to upgrade if I don't have a clear need for that?
(NOTE: I understand developer's point of view and desire for uniformity. But I'm arguing from consumer point of view).
"Who actually wants to haul garbage for a living? Or clean toilets?"
Machines would do without problem.
Who will want to repair those machines?
"This generation may be the one that will face Armageddon." -- Ronald Reagan, "People" magazine, December 26, 1985