It's looking more like the knife attack on Americans in Beijing soon after the start of the Olympics has little to do with the victims being foreigners and everything to do with them being a happy family. It appears that Tang Yongming attacked them because he had severe family problems, and seeing a happy family with two parents and their daughter may have triggered a rage that made him attack. Or perhaps he was planning to attack any happy-looking family from the start: it would explain why he was carrying a knife. If this speculation is true, then the timing of the attack coming soon after the start of the Olympics may simply be a coincidence.
While the attack is still inexcusable and does not lessen the tragedy the family has suffered, it would at least indicate that there shouldn't be a repeat of the attack. The good news is that the condition of the wife is improving, so hopefully there will be only one murder victim, which is bad enough.