Participating in TC50 is not as prestigious as participating in YC, but it is not trivial either. As a reader, I care about whether a company launched at TC50.
The "TC50 startup" thing just seems a bit like newspapers who constantly feel the need to remind you that they broke certain stories "As previously exclusively reported in this very paper" etc.
Just because someone launched at a certain venue, doesn't mean that venue can really claim any ownership. But then it's a common enough thing - you get stars/singers/actors who are constantly labeled as 'being discovered by X' which must be pretty irritating for them.
sorry, went off on a rant there :/ just my 2c
To quote the Clash,
"If Adolph Hitler, flew in today.. They'd send a limousine anyways"