I came across this problem quite sometime back - probably a year or so back.As you have mentioned, if you change the primary
DNS to x.x.243.70, it works fine - but with others, there are issues not only with msn, but with a few other sites also. (At least there used to be issues - have not checked of late). The site is not blocked, but just a DNS issue. In fact, going a few more years - around 2005 I used to face this problem with a lot of sites - I had to solve the problem then by using VSNL DNS on MTNL connection

-- used to work fine. I switched back to MTNL DNS about a year or two back when they had more or less solved this issue. But this MSN issue is still a problem for the last one year or so - many of my friends face this problem, and I ask them to change the DNS - and it works fine.