The problem is that people equate consoles with the games on it, which is something you cannot do with Sony and Microsoft. Sony and Microsoft do not produce games themselves, they hire second-party developers to make exclusives for them. Nintendo on the other hand makes their own games. In this vein, Nintendo is the greatest console gaming company out there. The Zelda series, the Metroid series (of which the Prime games are the best), the Kirby series (Epic Yarn was great, I don't care what others say), the DK series (DK Country Returns, heck yeah) and the myriad of Mario series (including Kart, Super Mario X, Paper Mario, New Super Mario Bros. X, and others). Plenty of always great games, as well as reasonable - but still pretty weak - third party support. Games like Epic Mickey stand out (a film student's dream).
That said, Sony has a great line up. The Uncharted series (made by Naughty Dog, which is owned by Sony, so second-party) is very alluring, though I haven't made the plunge yet. MGS4 is one of the games of the past decade that I shoot myself for missing out on, and I plan to get my hands on it as soon as I have the funds. Other than a few other dark horse titles (Heavy Rain comes to mind), though, I don't have that much love for them. Microsoft has never really had me. Halo was a great game; the series, not so much. Gears is far too gory for my taste.
But, with that said, I will always - always - prefer the PC to any console. PC gaming is far more versatile as its limits are constantly evolving, whereas a PS3 has the same limits now as it did when it launched in 2006. Shooters control best on the PC. And the best devs do their best work for the PC. Bethesda, BioWare and Valve have my undying love, with Portal 2 being my (new) vote for the best game of all time, with Ocarina (it's too revolutionary to be excluded), Elder Scrolls IV and Mass Effect 2 not too far behind.
BUT - there are some experiences that you just cannot have on the PC. And that is precisely why I will always buy the Nintendo console when I can. Motion controls don't work on the PC, and Sony and Microsoft's motion controls are mostly gimmicks. Hence, I have a Wii, for games like Epic Mickey, Twilight Princess, Super Mario Galaxy (both), and others. Double screen technology with the power of a console? Yeah, sorry PC, gotta have that.
TL;DR? Nintendo will always have my money for console and handheld gaming, because they offer novel experiences. Otherwise, 90% of my gaming is PC.