In PvE, people generally go for superior runes because that's the only way to get 16 points in an attribute. If all those copycat SF eles started only running 15 in Fire instead of 16, they'd be noobs of course.
In theory, a bit of coordination in PvE teams can allow the 'nukers' to avoid being targeted, and so it's worthwhile them increasing their damage output at a cost of health. For 'tanks', it's better to go for minor runes, to sacrifice damage for health - because the latter is more important. A lack of minors being used may be a consequence of there being little middle ground. If people are going to sacrifice some health, may as well go full bore.
If you're not planning on running 16 in an attribute, two major runes are better than one superior - the health cost is five less. From my personal experience, though, I always ran either a 14 att and full health build, or 16 att and reduced health build. I didn't feel it particularly necessary to go inbetween.
It may also be a consequence of when major runes used to cost 50 health, not 35. Then it certainly was not worth that expenditure just for one attribute point. To gain a second point, you only needed to sacrifice an extra 25 health, which was more reasonable overall: an average of 37.5 health per point, not 50.