Found out the cause; If you are using SLT ADSL; you cannot reach any of the google hosted contents using a custom domain name. SLT as usual; has screwed it up.
May be they are taking advise from China and are in the process of blocking out Google.. or whatever. In all accounts.. fuck SLT; they seem to even block the Google's DNS server IPs.. I was using 18.104.22.168 and 22.214.171.124 as my DNS settings and I was experiencing a lot of failures in DNS resolving. Didn't suspect SLT. I just switched to SLT DNS servers and lot of things got corrected. But who knows.. may be they are monitoring my internet usage too.
You could use a custom proxy for now to access all those unreachable blogs with custom domains.
But long term... complain to SLT. Make demands. Or let's just switch ISPs.. Dialog?