In an ongoing effort to ensure (the guise of) safety in the NFL, the league's ownership group by way of its competition committee has approved a rule, taking effect in 2013, that will require all players to wear knee and hip pads.
Many players forego that equipment now, usually citing a lack of comfort and need.
The league said the year delay in putting the rule into effect gives equipment manufacturers time to enhance their products, in an effort to alleviate players' concerns with comfort.
It's an interesting decision overall, considering the safety banner has been waved over the players' heads, so to speak. To this point, all the talk of improved safety has been focused above the shoulder, but apparently, hips and knees are getting their day in court now. I'm not a doctor, but I'm fairly certain Steelers RB Rashard Mendenhall's torn ACL would not have been prevented if he had a better knee pad (or even one at all, although it appears he does wear knee pads).
The league's point, though, may be more in the delivery of hits from offensive players to defensive players. Taking a knee to the head when that knee is padded is probably less severe of a blow than one from an unpadded knee. That wouldn't explain the hip pad, however.
In the end, it appears NBA players have more leg padding than NFL players do, and while most of that is due to the fact they play on wood and not grass or SportTurf, it is difficult for them to address safety without stricter rules surrounding equipment. Maybe this is the first step toward that end, which is probably the right direction in which to go. Players are required to wear those pads at the high school and collegiate levels, so it's not as if it's totally unfamiliar ground.
The NFL Player's Association has said they will weigh in on the matter, but considering equipment is considered an in-game issue, it's left to the discretion of the owners, according to the CBA.