Warranty: depends on your location and the relevent consumer law there

Depends on the consumer laws where you live.

In the US, the only way a warranty can be tied in to service with the
dealership (you have to go to the dealer in order for the warranty to
be valid) is if that dealership provides the service for free for the
lifetime of the warranty.  (look into the Magnuson-Moss Act:
http://www.ftc.gov/bcp/conline/pubs/buspubs/warranty.shtm )

For the vast majority of automobiles in the US, that means that you
can have the services performed at any dealer, independent mechanic,
or even DIY, so long as you can prove that you had the services done
appropriately/timely, the manufacturer cannot deny you warranty
coverage based solely on not going to a dealer.

On http://www.lexus.com/models/ES/service/schedule_maintenance.html ,
Lexus only recommends seeing your Lexus dealer, and then extolls the
virtues of seeing the dealer...  They don't say that going to the
Lexus dealer is required.

I'll note that according to the Scheduled Maintenance Log,
http://www.lexus.com/pdf/service/Sedans.pdf , that the first service
at 6 months/5000 miles is complementary if performed at a Lexus
dealership, so only you can decide if that initial oil/filter change
and tire rotation (any shop can do this or you could DIY) is worth
your time/hassle of going to the far away Lexus dealership.  The first
service where things might get tricky for a DIY or independent is the
36 months/30,000 mile service, where the brake fluid needs changing.

Do you have a Toyota dealer near you that has a good reputation?  If
you don't have a Lexus dealer near you, a local Toyota dealer can
request Lexus/Toyota to do warranty service. As for maintenace, Toyota
can do it, at an hourly labor cost considerably less than Lexus
charges, at least in my area. And, personally, I get better service at
my Toyota dealer. When it comes to servicing my car, I prefer "meat
and potatoes" to "internet tech".