I completely agree but would not expect a receiver that just made a really big play, and expended a ton of energy to take-on an unnecessary hit for a couple extra yards. Factor in his lack of size, age and recent-injury-history, I was OK with Jackson going out-of-bounds. He did exactly what the #4-WR / deep-threat was supposed to do.
Also, that was a huge play in that game. it was the third quarter, and the Rams were trailing.