Canon has been working a lot on cinema lenses. Their broadcast group does not seem to be directly involved, so the DSLR design and production has been bogged down. Nikon also has a lack of resources for designing new lenses. Apparently, Sigma has added resources(Tooling, manufacturing, and designers) to put out a lot of new lenses. This is probably hurting Nikon more than Canon, but both must be feeling pressure.