Well not exactly
I have a private 13" MBP and 13" white Macbook and a business 17" MBP - it's an old model, the 1st with Intel.
Anyways, I can't imagine working on a 13", since I have a couple of apps opened at once: Catalox for copy input, Lotus notes, Adobe Bridge, Indesign, safari, word, excel, powerpoint. And the 17" screen is the only way to go with all this.
Whereas at home I use computers for my private stuff, so the 13" is absolutely enough for Safari, Word etc and I use my TV to play movies either from the MBPs or from my hackintosh desktop.
So in your case it seems that 17" is a good idea - then again art directors at my company often use 17" MBPs and plug them into external displays - using only the external. Print production team on the other hand uses the same set, but they take advantage of both the MBP screen and the external LCD display since they need more space. So it obviously depends on what you need. If you don't care much for mobility - I mean "easy" mobility of 13", since the 17" is still mobile, though not that convenient to move around - then get a 17". If you care for mobility then maybe go with the 13" and an external display. And if you don't want to spend extra $ on the display then using your TV may also be a good idea depending on working conditions that gives you - I have my TV far from my desk, so it's not to comfortable working on it.
PS. I bought my 13" MBP just hours ago, but before making a decision I was considering getting the 15" model. But when I compared them at Apple store I came to a conclusion that the 13" will be sufficient for my usage (I have the 2,8 GH version) and more mobile than the 15" since it fits into the laptop bag I already own

I travel regularly from the city that work in to my place of birth, so the 13" is perfect for me. Plus doing the things I usually do at home don't require that much computing power, therefore I felt that buying the 15" would be just a waste of its potential, since I have my business MBP for the hard work.
So there hope that helps in any way.