First of all you have to realize that there is no way the dealer would notice corrosion on the inside of the rims when doing routine maintenance. You'd have to dismount the tires to see the inside of the rims, and they don't do that routinely.
You also have to realize the dealer does not decide what they can cover under warranty. The vehicle is out of the waranty period, and its up to the Lexus regional rep whether or not they will cover it. The dealer gets paid whether the warranty covers something or the customer pays, if the warranty is in play Lexus pays the dealer for the work.
Now understanding this, you should not be angry with the dealer, you should try and work with the dealer to get Lexus to cover the repair (which they should and I bet they ultimately will do). You have to stay calm and professional, but very stern and unyielding in your expectation that Lexus should cover the repair. Ask to meet with the regional rep in person and make your case to him, the car is 2 months out of warranty, this is something that has never happened to you with any car you've ever owned and although you would like to remain a loyal customer of Lexus and of Lexus of Sarasota, if you're stuck with the bill for this repair you won't be able to do that.
They'll cover it.
Other option is to just buy four (or however many are leaking) RX330 wheels on eBay and replace them yourself, that'll cost a lot less than $2,000 or even $900.
This is an entirely different situation. Those must have been aftermarket chromed wheels. Thats very common, the finish starts to bubble and then they start to loose air. No reason Lexus should cover failure of aftermarket chromed rims, and your vehicle is significantly older than the OP's vehicle and longer our of warranty.