I believe the standard rooms are booked en-mass by the tour groups, and given the high occupancy of that category on specific dates, there aren't any discounts for them. I think how it usually ends up is that the mainlanders in tour groups are segregated into standard rooms, and everyone else gets the superior rooms. It's probably not intentional, it's just the results of their block bookings.

Never tried checking in at the lounge myself. I think they expect plats to also check in at the lobby, as they always have the paperwork ready there - details pre-printed, vouchers stapled to the form, etc.