Is he closely tied to Nintendo? Not really. Does he show up a lot on Nintendo systems? Not particularly.
It's not like SF2 made the best-selling SNES games list three times, or Nintendo held an event for SSFIV3D's launch, or Mario's moveset in Super Smash Bros is inspired by Ryu. Ryu's been on just about every Nintendo system at least once. Not counting bootlegs, we have:
Every iteration of Street Fighter II on SNES and Game Boy, and Wii VC if you count that (and if you do the original Street Fighter's on there too).
Street Fighter Alpha on Game Boy
Street Fighter Alpha 2 on SNES
Street Fighter Alpha 3 on GBA
Super Puzzle Fighter 2 Turbo on GBA
Capcom Vs. SNK 2 on Gamecube
Tatsunoko Vs. Capcom on Wii
Super Street Fighter IV 3D Edition on 3DS
Project X Zone on 3DS
The only Nintendo consoles Ryu hasn't made any appearance on (as far as I and Google know) are the NES, Virtual Boy, N64, DS, and Wii U. And I'm pretty sure he was in that Capcom Vs. SNK Card Fighters game on DS, so that leaves 4 out of 12 systems, 3 out of 12 if you count Street Fighter as a whole (Street Fighter 2010). Ryu's been on nine Nintendo systems, beating every other third party but Mega Man (Snake's been on 5, Sonic 6, Pac-Man 8, MM's been on all of them but the Virtual Boy). To say Ryu doesn't show up on a lot of Nintendo systems is to say nonsense.
Street Fighter 2 and arguably the first Street Fighter, also popularized the fighting game genre and also inspired many other fighting games, Smash being one of them if you want to call it a fighting game. I'd say the icon of fighting games fits in a fighting game.
Was he asked for or wanted? Not in the least..
I'm glad you know who everyone did and didn't want. I guess that Ryu support thread from 2013 isn't there, and I guess the occasional people I see elsewhere say "Ryu'd be cool in Smash" don't exist. Every character will be wanted in by somebody. You can bet your ass someone out there wanted Wii Fit Trainer or ROB.
That being said, I don't mind Ryu being in, if he ends up DLC. I'm not a big fan of Street Fighter but it's kind of neat to see how a more traditional fighting game character would play in Smash. Plus, Ryu's theme just gets me pumped the hell up: