Only because I'm feeling particularly argumentative
Canon has never chased anyone. They never chased anyone in the past, and they are not chasing anyone now. Canon were pretty quick to chase Sony's camera division (previously known as Minolta) when they introduced auto focusing SLRs. The Minolta Maxxum 7000 came out in February 1985. By the end of 1986, Auto focus SLR's accounted for more than 50% of SLR sales and was dominated by Minolta and Nikon. And where was Canon? (hint: The T80 doesn't count...)
Well, if you want to get right down to business. In the late 70's, Konika released a camera with a passive AF system. Everyone else followed suit, and released cameras with the same kind of AF system. Canon? Instead of simply "responding" with a "me too" product, they innovated...and created the first active AF system capable of focusing in the dark.
The T-80, which does count, as it was well into development and just about ready for release when the Minolta AF cameras were released (I mean, it was less than two months later that the T80 hit), was Canon's first modern-ish DSLR AF system and was obviously in development for some time before it's release. That was 1985.
Canon released the first EOS in 1987, two years later, with a completely new CAMERA SYSTEM designed from the ground up. We aren't just talking AF, were talking about the platform that Canon launched to fuel their camera systems for decades, the same system that their current modern cameras are based on. Were talking about a mount system, a flash system, a camera system that spawned Canon's entire photography ecosystem. It takes more than two years to plan and develop such a huge thing, so one has to assume they were already working on it by the time the T-80, a-7000, etc. hit the streets.
So, did Canon "respond" with EOS, an entirely new camera system, just because of the a-7000's AF system? Or did Canon innovate their way into total dominance with a camera system built for a new era from the ground up to support the things their customers demanded? Personally, I think there was a little bit of both "response" and a lot of "lets build something kickass and new that will triple our bottom line". It just takes too much time to R&D up an entirely new camera system from scratch for it to just be purely in response to the AF dslrs that hit in '86. The plan had to have already been in motion before hand.