I had some non tyre-related issues with my first IS200 back in the early noughties and instead of writing to them, I rang the head office and asked for the then MD's fax number. A fax was duly sent with spleen in full vent mode, and two days later I received a letter from the MD and a free service voucher.
Regarding the tyre wear issue, I must have spent about a grand on new tyres on my two IS200s during the time I had them. It's my own fault - I joined the Owners Club in '02 when I got my second IS200 but then I let my membership lapse. Had I not done so, I'd have found out that Tony at WIM could have set the car up properly. The local people I use for tyres and tracking know what they're doing, but they only have the data which Lexus give them to do the tracking. Every time I went in to have another set of scrubbed away fronts replaced, they'd say that the tracking was "within limits" and that they'd seen many IS200s with the same symptoms.
As for your expected reply, can you be sure that they haven't replied? Perhaps it has got lost in the post. Do you have proof that it arrived?
And as Scorps says, you should check your tyre pressures/wear every week.