Who ever said he has to be using a Katana all the time? For all we know it was simply a falchion blade now and again. They are curved, after all, and though I'm only guessing, I'd wager that a Katana could fall into a loose defenition of falchion. After all, would the Star Sword have been a Katana? Why would those have Zeal forged such things, and also the long swords that seemed to also be existant?
Personally, I think the thinner Crono looks kind of neat. But seeing what people have said, I think I'm in a minority. And, actually, the photoshopping isn't THAT horrible. Hey, at least they made an apparent effort. It's far better than some we've seen over the years.