Plus, EF-S lenses concentrate at the wide-angle end of the focal length spectrum. Beyond wide-angle lenses, it's easy to substitute a full-frame lens for an EF-S lens. Is a 70-300 mm lens a full-frame lens or is it an EF-S lens? It depends on the camera it's on. I was going to say that but there it is already.
I think the relative lack of interest in EF-S lenses is that most of it is well covered already. You have cheap zooms, wide and tele, and less cheap standard zooms too. What gaps are there? I think some cheap EF-S primes will help keep up with Sony and Nikon e.g. 30/35mm f/1.8 and a 8-16 would keep up with Sigma. On the long end, you can go EF lens easily.
I don't think this is true at all.
I know it may surprise some, but for a lot of us, APS-C is a virtue. For the same parameters (focal length, aperture, build quality, etc.) an APS-C lens will be smaller, lighter, and cheaper than an APS lens. Those are all good things.
To us, it's not a good answer to say "Oh, if you want a decent quality telephoto zoom just get one of the 70-200 mm or 70-300 mm variants". Doing that compromises on size, weight, and price.
But just because we want smaller, lighter, and less expensive lenses doesn't mean we want to compromise on quality. Canon has plenty of cheap and cheerful EF-S lenses, but the high-end ones are rarer: the 17-55 mm (obviously), and the 60 mm macro. The 10-22 mm and 15-85 mm are also well regarded, but the lack of constant apertures IMO leaves me wanting.
As it stands, Tokina's got my money for an ultra-wide, and I think there's a good chance that Sigma will get my money for a telephoto (the new 50-150 looks very tempting). Likewise a prime: the Sigma 30 mm f/1.4 is probably the best option.