There are a lot of things that can contribute to whether you are successful at an interview or not. Sometimes there is a better person who comes along - it happens.
I've been on the merry-go-round for a few months now (coming up to Christmas is *never* a good time to start looking in the IT world... well, in Australia anyway....) and I have seen the range of methods people use. There are those who ask dozens of technical questions (no problem) but were asked by a HR person who had no idea what I was talking about and transcribed those answers into a report for the hiring manager. Things can get lost in translation but, to her credit, they didn't and I scored an interview.
Like every other industry, as you get older, the panels look younger and you suddenly become aware of your age and that oldies aren't like anywhere in the job market. If you don't stay on top of the technology and add value to yourself all the time, the knowledge will pass you by and the scrap heap beckons. So, yes, the onus is on you to ensure that you retain that value in yourself and not expect your "brand" to be the saviour every time.
The worst interview result came from a company that wanted a senior DBA. I seemed to get on OK with the panel and was professional in how I handled things. I answered all of their questions and didn't allow ego to be a problem. I even quizzed them on their "difficult" system which they told the recruiter was a tough one (it wasn't). What cost me the job was being reserved and not acting like my name had just been called out on The Price is Right and running around like a loon while drooling and professing that I had always wanted to work with this company that, quite frankly, nobody knew about (I know this because I asked many of my old colleagues....)
It doesn't help your career when you have start-ups that think they are so great that it is impossible to not know who they are.
A lack of planning on your part does not constitute an emergency on mine.