IMO the city inspector was right (on the CSST) if he was an "electrical only" inspector. Bonding of the CSST is not covered in the NEC, it is required by the CSST listing, and should be the responsibility of the CSST installer to ensure it is done, and whoever is responsible to inspect gas codes to enforce it. Of course a "home inspector" is typically wearing both hats to some degree. (Full disclosure; I copy and pasted the NEC and NFPA info)
IMO a HI is nothing more then a tool for finance companies to use for leverage when underwriting mortgages. In general the HI has no "authority" to demand anything be changed, he is just writing a "report card" of the condition of things in the home. Buyers and sellers can use this report for negotiating but no deficiencies in that report are legally required to be changed. Finance companies and even insurance companies however will refuse to work with you sometimes if you don't comply with what they want - and that is "free enterprise" you can possibly find a finance company that won't make you change anything, or maybe pay a higher interest rate or a higher insurance premium.
Buying a previously lived in home is like buying a used car. Things do wear out, need replaced/repaired, and there usually is no warranties, yet mortgage companies seem to expect the home to be "like new condition" according to inspection reports or it raises red flags
A 10 year old home is typically still a fairly new home, but likely does have code issues that have changed since it was new.
A 10 year old used car - much more common to be used beyond it's intended capacity, and safety equipment (if still functioning correctly) also has been superceeded in new car standards - but the car is still legal to drive at it's original standards.