Every headphone measured and posted on the Headroom site has a little bit of the same looking non-flat curve due to the (excellent) measurement technique, and also due to the fact that a headphone that measured truly flat based on their measurement technique would really sound BAD.
But the bottom line is that the t50p is certainly going to have a noticeable character to its' sound based on the FR, and in fact, it does. That said, who cares? All headphones have a character to their sound. All that matters is if you like it. It would have been better, IMHO, if they had found a way to knock 10db off that 8 kHz peak. The T1 has a treble peak, too, but it's at more like 10 kHz, which will be less noticeable, and it's a much smaller peak.
So true. In fact, I recall seeing a graph that showed what the ideal headphone response should be and it was far from flat, there was a huge dip in the upper midrange. My favourite headphones have a very ragged response on a graph. The ones that come closest to a flat response are the most dull and boring.