At Mridula's suggestion, I called up the Spectranet's Call Centre in Delhi, and their agent told me that the Ministry of Communications had indeed sent a letter asking them to block the blogspot.com sites. He was unaware of the reasons behind this move.
So, blogspot-blocking is real, but appears (at least, as of now) to be localized. In Bangalore, for example, I have been able to access both my blogger account and blogs on the blogspot.com domain from my home, where I use BSNL dial-up.
If you have any clue about what's going on, do please head over to Mridula's blog and leave a comment. She has been following up on this one.