I've always been frustrated at the expectation that every character should have high Fortitude and Will defenses, even at 2/3 of the normal cap. Will can kind of make sense, as you'd expect the heroic types to have higher-than-normal willpower. But Fortitude just never seems justified, particularly when we consider values of 0-1 are considered "average human," and that it's not common to expect normal people to just have unusually high physical resistance to poison, disease and such.
Fortunately, in the games my group and I play IRL, Fortitude and Will attacks are rare enough (and Fortitude more so than Will) that it's not a real issue. Normal human PCs can have Fortitudes of 0-4 and it very rarely impacts play; even when a villain with a Fortitude-targeting attack crops up, the "normals" are more apt to let the more resistant folks handle him while they focus on other areas.
However, in games where Fortitude attacks are almost as common as Toughness, that can easily be a problem. And to my mind, just saying "please buy up Fortitude" always struck me as a rather nonchalant, inconsistent response (especially when coupled with insinuations of minmaxing--it's never made sense to me that having a low Fortitude could be considered powergaming, when the solution expected is to literally remove a clear, relevant weakness to the character in direct violation of the character concept.)
Forcing Fortitude (and possibly Will as well) to be bought up explicitly via a power like Toughness seems to address this very well.
Most sane heroes aren't going to just run out and fight crime without adequate resistance. So if they don't have enough speed, agility or whatever to evade attacks, they'll wear body armor, or do whatever is needed to allow themselves to survive being hit--effectively, hitting their caps, or at least coming close. If Fortitude attacks are almost as common as Toughness, then you'd expect that they would similarly take that into account before donning a cape--if they couldn't evade such attacks well enough, they'd take some sort of precaution against being harmed when struck by them (special suits, a Fortitude-enhancing elixir, a tweak to their power-based defenses, whatever.) Forcing the defense to be increased via a power keeps the base, unempowered Fortitude reasonable for a normal human character, and shouldn't be any more strange than a normal human going out of their way to beef up their Toughness in expectation of trouble.
Again though, I do think it's easier to justify a direct purchase of high levels of Will as it's a mental trait. Just as the normal human range for Intellect can be fairly wide (geniuses exist, and I'd think they would start at Intellect 5 at the low end,) I think the same is true of Will as well. Plus, it seems like it would be much harder to explain how a non-psychic power or device would somehow boost one's Will.