Not only is Nintendo constantly and consistently producing new IPs they are the only ones out there create new genres!
Brain Training/Academy created a new genre
Nintendogs created a new genre
Wii Sports created a new genre
Wii Fit created a new genre
Wii Music (and electroplasm) tried and failed to create one (hey, no one is perfect)
Plus many others
They've created lots of new IPs in existing genre's too but a lot of the Wii ones have never made it to NA.
There's little validity in creating new characters for new IPs as it's harder to market than using well established existing characters.
Nintendo is also a master of versatility with their characters. Look at Kirby: Epic Yarn - that's not a typical Kirby game and was originally a new IP but it works perfectly for the cute pink puffball. Link did Crossbow Training, Donkey Kong was on Bongos last gen, Mario is the ultimate master of all trades.
On one hand, it would be nice to see some fresh blood, but on the other Nintendo understands the power of maintaining their brands and unquestionably it works. 25 years later people still love Mario so much they'll buy a rerelease of a rerelease even with horrid antiquated graphics, even by Wii standards lol.
The reason Sony needed new IPs was because they didn't maintain their old ones well enough (Crash anyone?). But while Nintendo is expanding the market and always bringing in new types of games to play, Sony and MS just keep repackaging the same old, same old, games time and again, occasionally with a fresh coat of paint (IP) but it's still the same games we've been playing since the PSX/N64 days. They're great, don't get me wrong, but hardly pushing the industry in new directions.
Nintendo always has a difficult position of having created so many great IPs over the years people are always clamoring for a return to: F-Zero, Starfox, Pikmin, Waverace, Pilotwings, Fire Emblem (the Wii one was also basically a GC port), Luigi's Mansion, Custom Robo, etc, etc. So far they have brought back quite a few classics: Punch Out!, Kid Ikaris, Kirby, Donkey Kong Country, (new) Super Mario Bros, etc. But every new IP pushes someone's favorite IP further down the line.