Ok, I have to preface this post with the fact that I have no love/hate for either company, but GGKoul.. you have a lot of facts dead WRONG.
First of all, the Sega Master System was available in the US, and it directly competed with the NES. I owned/still have both and I live in good old NJ. They were both widely available and were direct competitors.
The 32x and SegaCD do not even hold a candle to the SNES.... 32bit means nothing if the product is a huge turd. I made the mistake of spending my hard earned lawn mowing money on a 32x. It was terrible. And it did NOT sell well at all after the first few months. The suckers (including myself) bought a lot in the first few months and that was that. The SegaCD did a bit better in the marketplace but really was lacking a lot. It was not a very good gaming system.... I doubt you'll find many people who disagree. It had a few good games, like any system does, but overall it was a huge flop.
Nintendo never did come out with a CD based system because it felt the market wasn't ready for it. That, and the SNES was doing so well there was no need. I'm sure you know Nintendo was working with Sony to create their SNES CD and broke ties with Sony. This lead, at least indirectly, to the creation of the playstation.
I agree GameGear was a good product and ahead of the Gameboy, but it wasn't necessarily the "better" one. I was lucky enough to have both, and loved my GameGear, but once it died in 2 hours, I went to play my gameboy for the rest of the week. Nomad was very cool though, I always wanted one.
As far as the GBA/GBA SP.... bad sales? What are you talking about man?

They have sold millions of those damn things. It's their best selling product. They've made a ton of money on GBA already, and the DS is selling like crazy too. Where did you even get that info?
Plus, you say that gamecube is trailing behind PS2 and Xbox, which it definitely is, but you don't even mention that your beloved Sega doesn't even have a system out.
And why on earth couldn't Nintendo make good games for other consoles if that's what it came too? There is a massive Nintendo fan base full of fan boys just like yourself. For every person like you who swears off Nintendo for no apparent reason, there are people who will buy anything they put in a box with a Nintendo logo.
Just as sega has Sonic, Phantasy Star, etc etc.... Nintendo has Mario, Zelda, etc etc. These games will sell no matter what system they are on.
I will never understand the fan boy mentality of "my system rules, yours sucks, and thats the way it is because I said so" Why can't you just like what you like without bashing other companies? There is nothing wrong with Sega, or Nintendo, or Sony..... they all make games. Some are good, some are bad. Some systems are better than others, and that can all change the next generaton.