If it's a battery problem, it can be corrected. If it's a design flaw, I agree it's a bigger issue. At this point, Apple is still investigating and it is still too early to conclude how big of an issue it will be for them.
There has been 7 incidents of swollen batteries reported so far. I can only imagine this is a very small percentage, compared to the number of units sold so far. Exploding batteries would for sure be a more serious issue.