The T-Dot was my baby. Larry's explanation of my background is slightly off, but a commendable effort. :-)
The EoTech was the CQB optic in our SOPMOD kits during my time frame. We used the bottom of the circle as an aiming reference up close because it's more precise than just holding off, but it's still slightly ambiguous. The T-Dot just "clarifies" that lower aiming reference. The 2 center dots vs one center dot decision was one that could have gone either way...the 2nd dot works great with a magnifier. It would be less cluttered when running without the magnifier with one dot.
Without a magnifier, and with the EoTech reticle turned up a little higher than optimal, the 2 dots become more of a "blade" and you can run it as such...top of the post = aiming reference. Incidentally, without a riser on a standard 2.5" HOB, the T is on at about 7yds. At about 15yds or so, the lower dot, or "bottom of the blade" becomes a useful reference, and then on up to the center dot and back down as the range stretches, but those distances will vary with ammo, barrel length, etc., and you really need to verify for yourself.
You can still "put the big circle on the target up close and press the trigger", but if you need a more precise aiming reference at across the room distances, the T-Dot is quite nice.