I still don't buy it. Of course it isn't a legal issue, unless SorryWatch was claiming trademark infringement (and I think they might have a good case if they wanted to assert a trademark and argue that ApologizeWatch dilutes their mark).
But as far as competition goes, a new competitor doesn't have a moral obligation to credit, or even acknowledge, a competitor. I didn't see anyone giving Facebook a hard time because they didn't apologize to Myspace. Even Engadget, which basically jumped into the exact same blogging niche as Gizmodo, had nothing to apologize for.
But I do agree with your point about SorryWatch using this to get some attention for themselves. They certainly have that right. Lots of people get attention for trivial things, and SorryWatch shouldn't be any different.