20 to 1 odds that the people you have talked to are WRONG, but unfortunately, even if you are right, argueing with the inspector means you ultimately lose.
Most inspectors are former contractors who learned thier trade under an apprentice system. They might not call it a master/apprentice relationship, but vast majority of trades are taught this way. They don't go out and get a 4 year college degree teaching them to be an electrician. Instead, they are hooked up with a more experienced worker who teaches them the skills. The only problem with this is if the teacher doesn't expand his (or her to be fair) horizons, then the student does not learn anything "new".
Originally, houses did not have smoke detectors, and people died. So smoke detectors became required and builders installed battery operated smokes. The public didn't change the batteries or took the batteries out, and more people died. So NFPA 72 (which is the basis of 99% of the fire code related laws) was changed to require power from the mains. Note that this does not mean they must be 110VAC smokes, just that they receive power from a continuos commercial source.
Every new house requires smokes, while most alarm systems (even in new houses) are installed as add-ins. So builders installed the easiest (and cheapest) means of meeting the requirement, which meant 110 VAC hardwired smokes. And the "master" taught the "apprentice" to install hardwired 110 VAC smokes. And because that was the only way he ever saw things done, it soon became "THE WAY" to do it, and therefore, "what the law requires".
I would give one more try to discuss (not argue) the issue with the inspector. Point out that this is NOT some cr*p you would pickup at Radio Shack. In fact, it's significantly better than the junk installed by ADT and their likes. It is a UL Approved Residential Fire and Burglar-Alarm Panel. It has
multiple approvals by UL, and is also approved by the CA State Fire Marshall. It is powered by commercial mains and battery power, and meets the requirements of NFPA 72. Stress that this solution is better than plain AC powered smokes, because 1) they are powered by both battery AND mains, 2) they can be monitered by a central station, and 3) they are supervised for wiring problems, power problems, and in some cases, dirt. Emphasize that you want to meet the code requirements IN THE SAFEST WAY POSSIBLE. Once they understand that you know what you are talking about and are not trying to take a shortcut, the majority of the inspectors I've dealt with will okay the installation. The better ones actually take the time to quiz me, so that they will be informed the NEXT time they come across something like this.
And if he still insists on 110 VAC smokes, well suck it up and impliment one of the solutions mentioned above. :unsure: