Well, at least the creator seems to understand the gimmickyness of the effect:

But please, use it wisely. If it starts popping up everywhere and becomes “that annoying javascript thing”, I'll be very upset.

Because some people deeply lust after the page turn effect. No accounting for taste...

Probably because he was sick of using flash to make something "flashy" that catches the user's attention. But yes, use this sparingly.