Classic & Vintage - why the 2 tooth difference in TA chainrings?

Ive noticed this on alot of TA chainring setups there will be two nearly identical large chainrings with only a 2 tooth difference, then there is the third granny gear. Now I understand the idea behind the granny gear... but whats the point in having two nearly identical large chainrings? Wouldnt it make more sense to have a mid sized chain ring? Ive always thought of the big one being for "super speed" and downhill... the middle for all around, and the small for climbing.

I think you're talking about half-step gearing, and the triple option: half-step plus granny. It's not always just a 2t difference between the chainrings, that depends on what you run in the rear. Rather than my trying to explain it, just do a search for those 2 subject lines in something like Sheldon's site.
Cyclocross cranksets also usually have a close jump between the 2 rings...

Maybe this will help:

http://www.sheldonbrown.com/gear-theory.html

Back in the 70's the Junior race catagory had a 93 inch gear restriction. I ran a setup of 49/52 chainrings and a 15-24 5 speed cog. Gave me a nice range of gears. And with the chainrings that close in size the front derailleur shifts between them very easily, not that big jump/drop of the chain. And when running through your gears you use the front derailleur as often as the rear.

Back in the 70's the Junior race catagory had a 93 inch gear restriction. I ran a setup of 49/52 chainrings and a 15-24 5 speed cog. Gave me a nice range of gears. And with the chainrings that close in size the front derailleur shifts between them very easily, not that big jump/drop of the chain. And when running through your gears you use the front derailleur as often as the rear.

I like what you said at the end there, that seems very interesting. I definitely tend to stay in one gear up front and shift the back.... but this makes alot of sense! and I can see myself liking it. Thanks!

I strongly favor a 3-tooth drop between the two (outer) chainrings, because this works so well ratiometrically with a 2-tooth progression back. One of the all-time classic combinations is:
49-46 / 14-16-18-20-23 -- plug that into an Excel and you will see why I like it so well. I took the concept a step further in the mid 1970s with my third-step gearing: 49-46-43 / 13-16-19-23-26, which provides a beautiful set of 14 ratios if one avoids large-large cross-chaining.

In the 1970s I geared my Nishiki with a 50-47 / 14-16-18-20-23 half-step, which I could change in 5 minutes to a 50-42 / 14-16-18-20-23 1.5-step for rides in the hills.