Is it just me, or is it usually/always cheaper to buy your domestic tickets in person at a Thai office, rather than online?

Example: today I looked up a economy HKT-BKK one-way online and it quoted me 2435+205=2640 baht ("Economy Restricted", dunno about the booking class). Later on the same day, I purchased precisely the same ticket at the BKK domestic terminal, and the price now came down to 1900+205=2105 baht (class V)! And this isn't just an isolated incident, I seem to remember getting exactly the same result for a ticket to UBP last year...