This is so true. I had the Red Cargo Train and the Yellow Cargo Train from last Christmas. This month, I decided to expand, and I picked up 2 Maersk trains and the Emerald Night. I am eyeing the Horizon now as well. However, all of my trains are sitting under a shelf right now because even after buy 3 sets of the 8 straight/8 flex packs (and having the track from the Red and Yellow trains), I still don't have enough to properly display all of the trains, let alone power them along a track.
Track is definitely the kicker. The first accessory someone who has purchased a Lego train set will be looking for is more track and if they can't get it easily the set will just end up on a shelf somewhere gathering dust.