My first response was to say bikes and dogs age different.

But then I thought about my previous bike and my last dog. Both required a fair amount of adjustment and attention when they were new but after we were used to each other both were fairly low maintenance and good company for many years.

But when age did catch up with them fighting the decline was hard and heart wrenching. My bike developed terminal Campy 8 non production disorder coupled with chronic rust at the top tube seat tube lug. The paint job that had been so pretty when new was rattle can sprayed over and scrofulous. When the big ring brifter broke on me and I couldn't easily find replacement parts I got rid of it and brought a new non rusting one home.

The dog developed hip dysplacia (sp?) and when he couldn't move to relieve himself I had to put him down.

I can't bring myself to replace him yet.