Since YouTube links are streamed instead of downloaded, there's no need to make a preview. You click on the link and will immediately see what it is. You also have the option to imbed the link like below, by using our flash tag:
https://www.youtube.com/v/wKivJBuTcYkCompare:
Embedded link:
[fl*sh=640,360]h**ps://www.youtube.com/v/wKivJBuTcYk[/flash]
Direct link:
h**ps://www.youtube.com/watch?v=wKivJBuTcYk
Look at the difference. I replaced some letters in the url's with symbols so you can see the difference between direct and embedded link, using our Flash tag.