I decided to check that claim, and I'd say it holds up reasonably well: http://vgsales.wikia.com/wiki/Biggest_game_system_launches I admit I'm eyeballing it there, but there isn't a great correlation between launch day/week sales and ultimate success.
Even the WiiU seems to have been at least a modest success upon launch: http://www.ign.com/articles/2013/01/11/how-successful-was-th...
Still, I would definitely take a strong launch over a weak one if I had a choice. :)