Capacity aside, I'm sure recent events might prevent some people from going on M:S. There are always those who need a tremendous amount of coaxing before going on a thrill ride for the first time, and hearing news that tragic will automatically put the ride in the column of "Never ever EVER" for many of those people. Especially because the ride is so new, there will be a concern that something important was missed. Maybe the ride effects people who just had exactly 12 ounces of soda 13 minutes prior while chewing strawberry-flavored Bubble Yum, and that could be me! I know it sounds facetious, but it is along the lines of how some people think, and until/unless they know exactly what happened to that unfortunate child so they know they are not at risk, there's no way many people of that type of mindset will ride.
Whereas, with ToT this week, the ride has been around so long, and with so few incidents, something like the young girl who (possibly?) had a brain aneurysm (thanks, spell check!) seems like an even more remote possibility. Hell, at this point, I'd think 95% of all people on that ride are repeaters. It has the advantage of a history behind it that M:S right now does not.
So I'd say the accident plays a part, but it's not the only reason why lines at M:S are shorter.