I just want to make the same point, but emphasise a different word. The cover letter should really stress the key points about HOW you are the person they want to look at and hire.
We used to get loads of applications with covering letters claiming things like 'I am a self starter', or 'I deal with pressure well'. Of course all the applicants will make those claims, even the people that can't back it up. Not providing evidence just leaves the employer asking the question 'how?'
For every claim one makes in the covering letter, one should justify it with real-world examples, e.g. 'my experience as head Wok-Smuggling controller at Acme Wok Co, dealing with multiple conflicting priorities under tight deadlines, shows that I respond well in a high pressure environment.'
I'd say the same goes for adding MA to the CV - if you can justify it, and it belongs to the group of skills and experience that illustrate HOW you are a good fit for the job, then go right ahead.