I will always like Reggie but he was a lot more hype than substance. It was cool when the Saints drafted him because it did feel like some sort of rebirth of the franchise as Ben said. Although Reggie was in N.O. during the best seasons in franchise history, not much of the success can be attributed to his on the field performance. There will be very little to no drop off with Sproles and the key stat to this whole Sproles vs. Bush argument is this:
Games missed due to injury the last 3 years:
Bush - 16
Sproles - 0
So Mike and Mike can think what they want, but when a guy can't stay on the field he gives you absolutely nothing (besides the fact the Saints averaged more yards and points in games Reggie didn't play compared to games he did play). Now Reggie may come out with a chip on his shoulder this year and do some good things in Miami, but if M&M would have done any research past performance would suggest the Saints will be fine (if not better) without him.
I am also assuming they didn't realize that by cutting Reggie, the Saints were basically able to get Sproles, Aubrayo Franklin (a top 10 DT in the league), a draft pick and a good special teams player. Reggie is a name brand so it is not surprising that uninformed talking heads would have that opinion, but when you look beyond the name it should be fairly obvious the Saints did what they had to do to improve the team.