It’s true that many Las Vegas hotels limit reservations, some to as few as seven consecutive nights. Why they do it, though, is a mystery -- not just to us, but to every front desk we spoke to, with one exception.
What we do know and understand is that most of the city’s hotels are licensed for transient commercial use, defined by NRS 116.31123 as "the use of a unit, for remuneration, as a hostel, hotel, inn, motel, resort, vacation rental or other form of transient lodging if the term of the occupancy, possession or use of the unit is for less than 30 consecutive calendar days." Thus, the state of Nevada restricts hotel stays to less than 30 days, not less than 12, 14, etc. -- despite the fact that many reservationists we spoke to claimed their hotels’ seven- or 14-day reservation restrictions are mandated by state law, which simply isn't true.
After 30 days, a guest is considered to have residency rights, which means both that it becomes difficult for the hotel to get rid of you if you won't pay, for example, plus they can no longer legally charge tax on the room. As to why most hotels limit the duration of a stay to 29 days or less, the person we spoke with at El Cortez was the only one who made sense, saying: "We limit stays to a maximum of seven days in any one calendar month, because we're catering to the casino, and most long-term guests aren't playing downstairs." Aha! That has the ring of truth to it, and explains why a hotel like Four Seasons, which has no gaming, told us they were happy to and had previously welcomed guests who stayed for months at a time, but that after the initial 30 days, you're required to sign a contract via their sales office.
Fortunately for those of you who wish to stay an extended length of time in Las Vegas, there may be ways of avoiding (or at least maneuvering around) the restriction. Some hotels allow guests to check out at the end of their stay, then check in again on the same day. Others permit back-to-back reservations, especially if the second reservation is made under a different name (of course, this works only if your traveling partner has a different name than yours). Still others advise that if you plead your case to a manager or supervisor, you may be granted an exception to the restriction. Be aware, however, that many hotels require you to check out for a designated amount of time (anywhere from a day to a week, or even three weeks, as in the case of the El Cortez quoted above) before checking in again.
The current writer once held (and perhaps still holds) the record for "longest-staying guest" in the history of the Rio, while working on a long-term documentary project. Initially, it was requested that I check out after the statutory 29 days, but they took pity and allowed me to keep the same room for five weeks, without having to move all my belongings and equipment. If you know you'll be staying more than seven or 14 days, you most likely won't be able to make a booking online, as the widget will block a stay that's too long, so you'll need to call the front desk. We haven't tried booking two back-to-back reservations online (if anyone has, let us know if it worked or not), but our advice would be to speak with a manager and organize your booking over the phone, as they may be able to bypass the built-in restriction (be aware that a phone booking may well incur a higher nightly rate that's available online, however).
If you're here for the long-haul, but not long enough to rent an apartment outright, then your best bet is to go with one of the number of extended-stay properties that aren’t restricted by the 30-day clause. Among them are Budget Suites of America, Extended StayAmerica, Emerald Suites, Hearthside, Residence Inn by Marriott, and Travelodge. Such properties offer weekly and sometimes monthly rates for visitors who don’t want to fork out big bucks for nightly rates at the Strip hotels, or who need a room for significantly longer than seven to 14 days. Note that you will pay tax on your room for the first 30 days; thereafter, no room tax is charged, but you will have to sign a contract, since after 30 days your residency rights kick in.