I like things the way they are, for several reasons.
One, numbers are dry and lifeless; they break mimesis, snapping the player out of suspension of disbelief. Outside of a few standardized tests, nobody actually thinks of abilities like strength in terms of numbers. It's a D&D bookkeeping trope that has somehow survived into a lot of other computer RPGs; in videogames, it should be avoided. When the computer can handle all the die-rolling behind the scenes, there's no reason to make the player deal with more than one or two numbers. Every console RPG has sheets of dry, pointless stats which players generally just ignore. They get in the way; it's better to just know who's tough and who's smart and leave it at that.
Second, following from that, the descriptive words are more memorable, easier to take in at a glance, and easier to keep track of in your head when you have a hundred dwarves in your fortress. With a hundred dwarves, who cares if your axedwarf's strength is 98 or 99? What matters is whether he's a strong-type dwarf or a tough-type dwarf, and brief, color-coded stat descriptors handle that very well.
Third, dividing it up like this into clear categories makes it easy to notify the player when things have changed. Sure, you could say "Axedwarf XYZ's strength has exceeded 9000!", but that would, to me, seem like a very out-of-place message... Dwarf Fortress' messages are generally worded to seem 'in-character', as if you were reading an actual book, written by the dwarves, that logged the fortress' events. Having 'reached 100 strength' written there would seem out of place.
Fourth, it would increase the game's learning curve (which it certainly does not need.) The words are self-explanatory; numbers aren't. Is 100 strength good or bad? How good or bad is it? "Extremely strong" tells you this. "100 strength" doesn't.
Essentially, exact numbers would give the player unnecessary, basically useless extra information which they would have to learn to interpret. It would make the game's interfaces and messages slightly more confusing. Good design principals focus on giving the player exactly the information they need, nothing more, nothing less; this goes sharply against that.
I would even, in fact, be against making it an option, or at least an official one. The reason for this is much simpler: Every little option, no matter how minor, is another factor Toady has to take into account when dealing with an already-massive project. Every optional feature or interface tweak is another thing that can break, and another thing he has to worry about updating to cope with future changes. A change to the interface layout might affect the word and numerical displays differently, say, and Toady would have to test each. For a 'feature' like this, it isn't worth it.
EDIT: Now, this doesn't mean that we can't convey more useful information in some other fashion, if that's all your worried about. For instance, if you want to be able to find the 'strongest dwarf' when you have a bunch of high-STR dwarves with the same descriptor... why not have a noble who produces a sorted list of the 'best' dwarves in a wide variety of categories? This would be extremely valuable for all sorts of things (say, if you want to grab your best surviving craftsdwarf after the one who was doing the job before dies.) This noble would presumably observe or test dwarves somehow, so while he wouldn't give you exact numbers, his ratings would reflect the fine differences hidden behind general descriptors.
Of course, the descriptors could also be extended at the upper end of the scale, or made more finely-granulated, if that's the problem.
[ November 06, 2007: Message edited by: Aquillion ]