Check out page 304 in the big owner's manual (4-3, Do-it-yourself maintenance, Tires). Lexus recommends utilizing the spare tire when rotating. The "rotate tires in the order shown" diagram shows swapping the spare with the right front and rear tires. Does the dealer actually do this when you take it in for maintenance? Sounds like the right tires will wear out much slower than the left tires this way.

 

I think it would only matter much for the 5-tire rotation if you have an AWD vehicle, according to TireRack.com.

"Five tire rotation results in equally distributed use that will help maintain equivalent tread depths on all five tires throughout their life. When applied to many four-wheel drive and all-wheel drive vehicles, this is required to prevent driveline damage if a flat tire forces a new spare to be put into service with partially worn tires on the other three wheel positions."

 

utter trash may have been a little harsh but OEM tires are generally low cost tires to the manafacturer that are "sufficient" to be driven on, far better and less expensive tires exist. Most OEM tires are very bad vs what can be purchased out there. Looking a little closer to the 235/55/18 MXV4 (only saw these in that size listed as OEM RX330/350) they are quite decent:
http://www.tirerack.com/tires/tires....e1=yes&place=2

Lucky you didnt get these on your vehicle, also listed as OEM:
http://www.tirerack.com/tires/tires....e1=yes&place=1

Was looking around some more for that size these were less expensive but have much better reviews across the categories:
http://www.tirerack.com/tires/tires....e1=yes&place=4