I was curious as to why the Hotel Reservation Girls don't have a more predictable travel schedule.  You know: HK for 2 weeks then Singapore for 2then Shanghai or wherever for two and back to HK on [date certain].  Certainly from a hobbyist point of view it would be convenient and might build a little extra repeat traffic if you knew exactly when a certain favorite would be returning.

Do they avoid doing this because of LE fears?  Or is it just too hard to execute/plan ahead?

well a lot of it is predicated on two things - how long they can get a visitor visa for in HK, and when their period is.

I'm not up on the visitor visa thing, but I think I read somewhere where you could stay up to 2 weeks in HK.  Someone else would be better able to answer this.

I think the maximium is 2 weeks but you may only get one if the immigration dude is having a bad day ... also frequent visitors can often get denied a visa/permit to re-enter which is why they cannot have a regular pattern ... that's what I heard from several WG's anyway ...

yeah its probably more of an immigration/visa thing than anything else. the mainland HGs would
be able to enter and stay in HK for 7 days max each time on a single visa. thereafter, they
return to SZ or somewhere across the border and wait it out for another 10 days while they
await their new 7day visa to get processed. they probably do this 2-3 times before they
'disappear' for a more lengthy period of time before returning again, precisely not to
establish a regular pattern that would draw an immigration officer's attention (there have been
cases where despite being granted a full 7 day visa, at the immigration officer's discretion at the
border, a 3 or 4 day entry is only given).

as for the european WGs, their visa regimes differ according to their nationality. if they happen
to be from an EU nation (e.g. poland where some of them do come from), they generally get
a 90 day visa-free entry whereas if they are from a non-EU state like ukraine or belarus, they
would need to apply for a visa before arrival. this is the same of the CIS states (i.e. uzbekistan
etc). again, they can be given a shortened period to stay at the immigration officer's discretion.