Now, now... no excusing the PSP's smaller sales on the lack of a holiday season
It's only natural the DS would sell more. It's cheaper in price and is backed by a company with a successful history in handheld gaming.
When Sony has released about 6 or 7 handhelds and it doesn't do as well, then you can blame it on holidays. But for now, you'll just need to accept Sony will have trouble swaying gamers who have enjoyed Nintendo's handheld legacy for all these years.