Personally, I've very rarely needed to replace those consumables, and I ride my bikes very hard. Only time I have needed a new chain and cassette is when I let my bike rust because I rode it all winter without washing it. And I've got like one set of brake pads in the last 5 years for my 2-3 bikes, since disk brake pads last pretty well forever as long as you don't foul them with something. I do go through a lot of tubes though, but no tires yet. As for tools all my bikes need for maintenance is a couple of allen keys and a phillips screwdriver.

I could see people spending that money bringing it to a mechanic for a tune up though. Personally I think that is a waste of money since it's super easy to tune up bikes yourself, but I do know lots of people who spent years with their bike shifting like garbage when it would take just a couple minute tune up to fix.