It may be hard to buy a new SD TV, but like I said they tend to last for decades so many people don't have an immediate need to buy a new TV. When they do buy a new TV odds are its going to be HD, but who knows how long it will take before that happens?
You could have made the same argument for the SNES. "Why does it need to support A/V cables when most people still have TV's that can only handle coaxial and will continue to have this for years?" It just doesn't make sense to completely ignore the TV standards available in stores right now. It isn't like the PS3 and Xbox 360 ONLY work on HDTVs. I don't have an HDTV so I hook my PS3 up with standard A/V cables. All this really is is an option.
We got the same sort of luddite argument with the Gamecube and online gaming. "Well there are a lot of people that still don't have access to fast internet." Well why should those of us who do have it, which is everybody not living the sticks, not be given the option? It wasn't like if Mario Kart was online everyone without fast internet could get nothing from the game. But instead we ALL were forced to go without. Much like online with the Gamecube the timing of the systems release was at a crossroads. It was at the time where the new technology wasn't quite widespread but it was clearly going to become the standard in the next few years well within the life time of the system.
I knew when the Wii launched that HDTV was here to stay. It was like Nintendo was six months off of SDTVs disappearing from the market place. They weren't thinking about the future at all. It was like, right now today, we don't need this, two years from now be damned.
Their decision to stay put, plus the decision to not go with online gaming on the Gamecube, is what ultimately creates the general fear that the Wii 2 will remain a generation behind. The Wii isn't truly a one-off. The Cube might have had up-to-date specs but their refusal to go online was one generation behind. The N64 is a pretty good behind-the-times console too. For three consoles in a row Nintendo has been incredibly conservative to the point where their decisions came across as incredibly short sighted and out-of-touch. The Wii is very much a product of its time in a bad restrictive way where it was something that reflected that exact moment but not even a year later. The Wii was designed for 2006 and maybe 2007 but certainly not 2009 and beyond. If we follow this trend then the Wii 2 will be a product of 2012 specifically for 2012 but ill-suited for 2014. Nintendo has to make something for something for 2016 and release it 2012.
And the funny thing is that back at the start with the NES, Nintendo specifically wanted something cutting edge that could last for years. If today's Nintendo designed the NES it would have been the Atari 7800.