I work at Target, and I can shed some light on why you think they're advertising it as temporary.
The system is in the ad due to the price drop. When stores print out signs to display the price of an item on the ad, a date will pop up on the sign. "price valid x/x through x/x."
These signs are made by the computer, which only knows that the item is on this current ad cycle, so it doesn't promise anything further. If the item was actually on sale, then that allows us to know when sales end easily, without having to scan.
On non-sale items, it just looks dumb. Apple products always have regular price signs on them. Despite being regular price, guests frequently will ask to buy "the iPod that's on sale." haha.