Trailing runner tagged out after lead runner is obstructed

[Dakota]

My initial thought (although I didn't post) was to consider R2 as a runner affected by the obstruction and award the bases. However, this part bugs me...

While it is true that in the umpire's judgment R2 would have scored had there been no obstruction, the obstruction did not cause R2 to not pay attention to where R1 was (or, presumably, the coaches) until it was too late and R2 was picked off.

Did obstruction cause R2 to not know where the ball was and where the preceding runner was? Does R2 get a free pass for such a base-running gaffe?

I get Steve's point of the defense not benefiting from the obstruction, but were they? Or were they benefiting from poor base-running by R2?