...I wonder why is it that Canon is investing so much in upgrading the superteles, rather than ~20 years old primes (e.g. 35mm f/2), in face of competitors like Sigma coming out with competing lenses (e.g. Sigma 30mm f/1.4 for APS-C & 35mm f/1.4 HSM for FF).
One big reason is the 1D X. By eliminating the 1.3x crop sensor from the flagship line, they (intentionally) created demand for longer supertele lenses, and it's no coincidence that they updated those lenses at the same time.
I would agree, except-
1. Canon could still introduce mkII versions of wide prime lenses, e.g. 35mm, 28mm, 24mm, and 20mm.
To go at it from a different angle, I was waiting for the EF 8-15mm f/4. Due to max aperture (I like f/2.8 on the EF 15mm for band shows) and price, I decided to buy a Sigma 8mm rather than upgrade.
Now, Canon did have an FD circular fisheye, it just decided not to make an EF version. It was f/5.6, but I would have considered it anyway.
2. The updated superteles are of the same focal length & max aperture the older versions, they are significantly more expensive, and the 1DX can't focus at f/8. If I had an APS-H camera, I would first look at a 7D, then at a Nikon D800. The last thing I would do would be considering a mk2 telephoto or a 1DX.
Which is why I think the olympics at the London is a much better explanation for upgrading the superteles.
Looking around at what I and photographers I know buy, it adds up to people choosing 3rd party lenses over Canon - Sigma 85mm f/1.4, Sigma 8mm f/3.5, Sigma 12-24mm (bought the mkI, than upgraded to the mkII), Samyang 35mm f/1.4, and so on.
People see what pros use on TV, but they also see what people around them use. This has the effect of 'Canon is good at making expensive lenses the rich media organizations buy, but hobbists are better off with Sigma / Tamron / whatever'
[As side note - I see lots of Tamron 18-270 in ads in newspapers and busses, and it sells well enough for local shops to sell in kit with Canon bodies. Olympus advertises on busses as well, and had the menus translated to the local language. Canon doesn't advertise at all, and I can't remember when I've last seen a rebate for Canon in any of the local shops. There's no denying local Canon sales are good, but I think Canon lens sales are heading in the wrong direction.]