Its not a coincidence the Wings were a bad team pre and post-Lidstrom, and were practically a top 3 seed EVERY year with Lidstrom.
As for the Norris winners being on "good teams", you could easily say that for the Hart, Art Ross, Vezina, and probably Selke too.
How the Wings fared before and after is irrelevant to the amount of talent on the team while Lidstrom was on the team though. He was obviously an awesome player, but having that much talent around him also meant he could play his game without overextending himself. On a lesser team it's unlikely he would be able to put up the same point totals while playing as well defensively, because he would have to take more risks offensively with less talent in front of him. We saw this a bit in '04, where the Wings lost a lot of talent and many Wings fans seem to think Lidstrom was trying to do too much instead of playing his game, which resulted in a poor season with both lower point totals and an uneven defensive performance by his standards. You'll often see this with other elite defensemen on weaker teams (like Doughty recently), and it probably hurt Leetch in the second half of his career.
In '01 for instance, he had 79 points, which led all defensemen as well as a bad Rangers team in scoring, which was 8 more points than Lidstrom and 20 more points than any other defenseman, yet he only finished 5th in Norris voting because his defensive reputation took a hit and he finished -18 on the year. Yet
@Machinehead has made a post in the past breaking down that plus minus, that it's due to shorthanded and empty net goals against and that the Rangers were a far better team at ES with Leetch on the ice.
I don't know if Leetch would have or deserved to win any more Norris trophies if he played for a better team in the second half of his career, but I think his career would undoubtedly be seen as better.