Now why would anyone buy The Bat! when free mail clients like Thunderbird exist ?

I work in two languages, English and French. The Bat! allows me to check the language used by the sender, and use the corresponding language template for the reply. A template can contain macros from the hundreds of macros available: set the date in French, clean up the subject line when it has multiple fwd: tags in different languages, quote the senders message and add the senders initials to the quoted line ( for example: PW> blah blah...) adapt the signature, and lots more.

So really the difference for me between The Bat! and Thunderbird is that The Bat! is geared towards professional mail users who don't mind tweaking it to death, whereas Thunderbird is more of a one-size-fits-all solution.