You're assuming that all BW fans are exclusively fans of the show, but this isn't true for everyone. Many of us are also fans of the toyline - remember that the toys did come first (oh the interesting 'continuities' I used to create with the toys before the show came out!). Remember that the toys already boast impressive sales - becoming the 3rd best selling boys' toy within its first year. A lot of G1 characters are still popular with fans even if they never appeared in the G1 cartoon, e.g. Whirl, Roadbuster, Top Spin, Twin Twist, Deluxe Insecticons etc. Yes, many of those characters did appear in the G1 comics, and Buzz Saw did appear in the BW comics too.
And keep in mind that a redeco is a low-investment cost for Hasbro since they've already developed the mould for Waspinator. They'd just be trying to milk more money out of that mould.
It's not done just out of greed -- repaints help to keep the cost of toys down. If Hasbro don't do repaints, then the cost of toys would go up. Redecos help Hasbro to milk more money out of the same mould which goes to offset the cost of R&D in developing these moulds. Also you have retailers like Wal*Mart demanding new product from Hasbro all the time, and redecos are a cheap and easy way to satiate that retailer demand without expending more money on R&D new moulds all the time (which would further drive up costs). Redecos are a "necessary evil" unless you're prepared to pay $50 for a Deluxe.
And I'll take Waspinator redecoed as Buzz Saw any day over another random repaint of Bumblebee! Heck, I wouldn't even mind seeing Waspinator redecoed with a G1 Bumblebee style head and called "Bumblebee" (seriously, it's a name that totally suits Beast Wars, and if they ever did Generations K-9/Wolfang, I'd like to see a redeco called "Hound" -- I've heard that Hasbro had lost the rights to those names at the time that BW came out which is why they didn't use them).