Both start the same way. A customer writes first, and that opens a 24-hour window in which the desk or the studio can reply freely, with photos, prices and questions, each reply charged at the service rate. The 24-hour service window explains the rule in full.
The difference comes later. A hotel's next message is a booking confirmation or a check-in reminder, sent days after the guest last wrote, so it has to be an approved utility template. A studio's is a dispatch notice for a painting that took weeks, or a note about new work to buyers who asked to hear about it, which is marketing and needs their opt-in.