You don't need to. I've only done the initial entry and not updated for subsequent trips. Also, on the last trip I had to do a new one as it had expired, and I put the hotel we were staying in the first night, but when DW filled in the customs form on the plane she put her sisters address (which we were travelling onto 2 days later).
You don't *have* to but DHS recommends that you do, therefore why not spend five minutes just doing it? Especially if you're concerned about US entry clearance anyway.
Your experiences are your experiences but you never know if you just got lucky or something, your situation is totally different, being married to a US citizen who is resident in the UK is rather different than visiting a girlfriend in the US multiple times in a short span.
DHS recommends you carry a print out of your ESTA every time you travel and it would look less credible if it had the wrong address etc if you needed to show it for any reason. If he gets pulled out for any reason and questions all of his official information would match up which again adds credibility to his story.
Ravenfurby, I always carried a letter from HR, you can print your own business card in a day so it's not very official, how about your latest payslip to show you're still employed?
