Those "Taiwanese version"s and such generally aren't the real thing. Unofficial/knockoff/pirated stuff is pretty common in Asia. I haven't personally gotten anything from Taiwan, but I know for sure that in mainland China, there's literally tons of that kind of stuff. $2 "Rolex" anyone?
That said, there are occasionally "International" or "Overseas" versions of things that you'd find on YesAsia and the like. They are generally only a little cheaper though.
Yes, it's true that there's a lot of pirated Morning Musume stuff in China, but recently, a Taiwanese record label (Forward Music) has picked up the right to sell Hello! Project stuff in Taiwan and Hong Kong. Their official website is here:
http://www.forward.com.tw/ (in Chinese). They don't sell the Single Vs, though the concert DVDs are all subbed. And yeah, the prices are generally much cheaper, the last time I checked it's possible to buy three Taiwanese versions than one Japanese version.
But I've also read some blogs which complained about the quality of the CDs. In general, the quality of the sound is good enough to not tell a difference unless if you have some sort of a super sound-sensitive audio system. I've never bought one (yet), so I wouldn't know. And I probably wouldn't know since I can't tell the difference between 192kbps and 320kbps with my headphones anyway ^^;;.