You appear to be missing my point as well, rbid.
TTL = Through The Lens.
s/TTL/through the lens/ in your last post and tell me there isn't a word missing.
"With the first DSLR cameras, through the lens was a technological problem..."
Through the lens what? Through the lens focusing? Through the lens flash metering? ??
While I think I know what you're trying to say, I have no idea what Mike was.
And, no, there is no special sensor in i-TTL, the matrix meter is used, which is why there are preflashes, because the matrix meter can't be used when the mirror is up.
d-TTL used a painted shutter to mimic film and used the old film-TTL flash meter, but had to preflash because the shutter isn't visible when the shot is being taken. ;) Point being I'm well aware of how the TTL flash metering systems work, but that still offers me no clue as to what word appears to be missing in the above posts.