Yes, and the mouse that comes free with every Dell or HP that I've ever bought or been given at work finds its way to the donations pile very quickly too. This is how mass-market computers work, and have worked since the 1980s at least.
One singular mouse design is never going to be equally usable for everyone. If you want to buy a computer without some of that money financing the production of a mouse you don't want, then buy a computer like a Mac Mini or any of the MacBook line which don't come with one. Otherwise, you are complaining about what you get with an iMac or Mac Pro; put it up for sale on eBay and get more money back for it that what it inflated the machine's cost by in the first place (which is, honestly,
maybe $5, probably $0 given Apple's price point strategy).
Um, I have considered that possibility, just not catered to it. I can't speak for Apple but given their work in the accessibility space I'm sure they have at least considered common disabilities.
And, yes, a mouse from Logitech doubtless works for you better than Apple's mouse. But not every mouse from Logitech, right? I say this because Logitech makes some mouses strikingly similar to Apple's Magic Mouse in ergonomics and design, as does Microsoft. Unless you are expecting Apple to have a box-to-order system with every iMac sold where they have you select from one of a dozen mouses they produced and put that mouse and only that mouse in the box before you buy it, you are just pissing in the wind here. Apple doesn't make a mouse for people with your disability; that is fine. Other companies do, and Apple's computers work just as well with those other companies' mouses as they do with their own Magic Mouse. It seems to be a problem with an as-easy-as-concievably-possible workaround.
More reason why you should buy a Logitech mouse. In fact, all the reason you should need, really
Not an expert in ergonomics says the ergonomics of something are bad. Gotcha. Again, if she doesn't like the MM, she shouldn't use one.
Whew, you finally made sense there at the end. Good for you, choosing the mouse that works well for you. Again, though, your three anecdotes (yourself, your wife, your daughter) do not add up to data. I'll give you four more anecdotes - myself, my wife, and our two oldest daughters all strongly prefer the Magic Mouse - and one more to bolster your claims - my teenage son hates it with a passion because it sucks for FPS MMO games. Still, not data. You buy what makes sense for you, and I buy what makes sense for me (for our household we use the Magic Mouse but my son plugs a $5 plastic mouse in for gaming). It doesn't need to be hard.
Apple's mouse designs have been along the same lines since the early 2000s (or was it even the 1990s when the Pro Mouse was introduced?) Fads in mouse design amongst other manufacturers have been all over the place in the intervening years, but two things have always been true: the incremental cost of the drop-in mouse on Apple computers has always been incredibly low because Apple produces just one design in astronomical quantities, and the purchaser has always been able to sell or even say screw the environment and throw that mouse in the trash and buy into any of the other fad devices if they wanted something other than what was thrown in.
Seriously. Go to eBay and search for Magic Mouse. Consider that if you bought a $1999 iMac and got a magic mouse "free", you can sell that drop-in for $35-40 nearly instantly, or have a listing for $45-50 stay up for a week or so before someone takes you up on the offer; you can then take that $40 and apply it towards any mouse of your choosing, which will plug into an available USB port or connect via bluetooth and work just as seamlessly in OS X as the Magic Mouse (without some features, of course, but other mouse manufacturers have followed Apple's lead with touch-sensitive areas). Consider that if Apple stopped selling the Magic Mouse altogether they would reduce the price of that iMac to ... $1999. Which means the "free" Magic Mouse really is free to you (not to Apple, but they aren't exactly hurting in the revenue department these days). To Apple, it is nearly-free marketing, a way to showcase the cool stuff and Apple computer can do out of the box, compared to the Dell with the $0.50 drop-in plastic yet still "non-ergonomic" mouse, which is why they do it. And, of course, there are enough of us out here who actually do love the Magic Mouse and its ergonomics to keep that eBay industry alive and prospering with more buyers than sellers.