Choi Siwon - Why is Siwon Singing the very first part of every songs?

if I watch the music video of super junior, Why is Siwon Singing the very first part of  every songs?

don't believe? let's see some videos of the following super junior ...
1. in the video bonamana Siwon sing first.

2. in the video sorry sorry Siwon also got the first turn to sing.

3. see no other videos below ... Siwon also had a turn to sing first.

4. not only in a video Super Junior. but in a video Super Junior M is the same. Siwon gets the first turn to sing. though Kyuhyun sing the opening part but a part of Siwon sing Cours1.

in this video too....
almost in every music video super junior Choi Siwon always get the first part to sing. hmmmm ... so curious?Why is Siwon Singing the very first part of  every songs?... here's the answer from Choi Siwon when asked about that question.

Mc : Why is Siwon Singing the very first part of  every songs?

Siwon : Staff and other members said that if i sing the first part of song, it's gonna be more succesfull.

ooo ... turned out that way. hihihi want to sing at the beginning or at the end I still like the songs ofsuper junior.