Not true [see edit below, retraction]. The apps I write and load onto my own devices outside the store stay on my devices until I get a new device. I think there might be a profile that has an expiration of one to three years, but in practice that never goes off for me. I either add a feature or get a new device before that goes off.

Edit: Ok, "true depending". If you are a registered developer then your apps last a year. If you are unregistered then you get one week, which would be a total pain in the ass.