Well, I saw many people having problem with Thunderbird not wrapping text at the default set 72 chars. Huh, I figured out the solution. The edit/options >preferences > composition > general tab has an entry box saying
"wrap plain text messages at __ characters"
the default set is 72 characters. Now what happens is that most of the mails that we send are HTML or 'unknown' by default. And the entry box says "plain text" not HTML. So, go to the most frequently mailed addresses in your addressbook in thunderbird and select 'plain' text message as the default in the contact details for each. :) it was not a problem, it was just obvious !!