50 seems a tad bit too low. There are now 30 skills per character, and you can still invest 5 points per skill. Assuming that you can start adding points to your character at level 5, that leaves 45 points to invest into skills. Well, 44 with the action skill being taken. This means that, at the very most, only up to 9 skills can be maxed out. I know there were quests that gave skill points, but I cannot see more than 4-5 points per playthrough, gathering a total of 8-10 extra skill points. So now we have 52-54 points to add to your character which equates to 10 skill points maxed out out of a potential 30. IF it is 50, I can definitely see Gearbox making it so that you only invest 2-3 points per skill and let a weapon or modifier add points to it. This is likely. However, it would be very interesting for it to be 70 for two reasons. The first and obvious reason is that you are getting more points to invest into more skills. The second is that the first game left us off at 69, and everyone who finished kindergarten math can figure out that 70 comes next. Hmm, I may have over analyzed this a bit, but it's fun to me.
Definitely over analyzed. Perhaps the big thing you overlooked was that 50 was the original level cap. The level cap wasn't raised until the third DLC came out. There are also only 4 skill SDUs (2 in Moxxi and 2 in Claptrap).
It's not as restrictive as you are making it out to be. The skill points you get solely for going to level 50 is enough to max out almost half the skills. That's still more than most similar systems would let you do.