Toyota Repair: Catalytic converter failure on Rav4 at 50K miles, extended warrantee, ac condenser

Question
I have a 2001 Rav 4 AWD maintained regularly per maintenance schedule, used normal conditions wiht 51,000 miles.  Engine light came on yesterday, went to dealer who says that the catalytic converter is in need of replacement.  (covered under my extended warrantee)  When I asked Why, only answer they have is, "we are seeing a lot of this".  They also want to replace the Cabin/air filter?   Last year, I had a rear shock that was leaking and that was replaced. (not under warrantee)   I never take car off road, drive normally, mixed highway and backroads, drive every day, use regular grade gasoline from numerous brand name.  In the fall, I did hit a deer and had to have radiator and ac condenser replaced...  that is the history and I can't understand why a cat conv. would be bad and worried that this is the beginning of other 'bad things' since the 'shock' replacement was also 'a surprise'. The dealer also says I should replace the spark plugs  now?  The regular service has been either at a dealer, or Firestone, and some 'quick oil' changes when I have needed to do it quickly to maintain the schedule.  (every 3500 miles).  
Sandra Jones

Answer
The Rav-4s are having some catalityc converter issues, there is a toyota service bulletin issued(TSB EG010-02) it involves recalibrating the engine control module(ECM)this is supposed to fix the PO420/430 trouble code, have the dealer look it up, it is still covered under the factory warranty, only after performing the service bulletin procedure and the check engine light coming on again should the converters be replaced, still under federal emission control warranty (8yr/80,000 miles)the spark plugs are recommended to be replaced at 60,000 miles.