Twitter less US-centric than a year ago.
According to Trendistic, last year’s Superbowl reached over 7% tweet-share at its peak:
This year, it was on the order of 4%:
This is not because the Superbowl was less interesting. In fact it’s very likely that it set a new audience record on TV. The explanation is simply that it is a very US-centric event, and Twitter is much less dominated by US users than a year ago.