I have only two reasons to greet someone on an occasion...1) The occasion itself, 2) To stay in touch. The last mentioned is more important of the two.
A few years back, I used to send every one an e-card (that is after having stopped sending paper cards by post). Now, I only send text mails or send a message to their phone, but I send a greeting nevertheless, whether it is the New Year, Deepavali, Christmas and any other occasion. I gloat over this because of a phone call received earlier this year. An ex-colleague called up to find out if everything was OK. I was puzzled. She said, "This year you did not send an SMS for Sankranti and Ugadi...so I wondered....".
I had to explain to that not-yet-married-blissful soul that I was a little busy with the brat and the rest of the family that it slipped my mind and nothing else.
After that I have been careful enough not to leave out any one, despite the fact that (expect on 'bigger occasions like the New Year) not many bother to send a greeting until one initiates. However, it is enough to trigger a response from those under hibernation!