Discounttrainsonline is the same way. The site looks like their inventory is enormous, but I wouldn't be surprised if 75% of the stuff is ordered as needed. The ship times are based on the estimated time it *usually* takes them to get the item from the manufacture, repackaged for an order, and shipped to the buyer.
I've ordered a few times from both sites, mainly track, because it's cheap. I ordered a bunch of n-scale rolling stock about 2 years ago drom DTO too. Orders on average took 2 weeks to get to me (1 week to process, 1 week in shipping). As long as you can hold out and wait, you can save some $$ with 'em.
I'll probably order from them again for my HO layout next year.
My Scenic Ridge kit came from wholesaletrains as well. It was listed as "ships in 24 hours" items, but didn't ship for about 4 days. But in the end I save about $60 over retail and other online places. So the wait was worth it, even though it killed me