I decided to write a post on why allowing embedded Videos in web sites and forum posts is a bad idea based on previous posts asking about it.

Here is why:
Embedding any object including Flash for videos is a security risk and is disabled on most forums for that reason.
Objects like Flash besides playing videos can also automaticly redirect users to a phishing site on load, open annoying popups, Show flashing banner ads, etc.
The same with Javascript and most objects that can be embeded including ActiveX controls in Internet Explorer and plugins for all browsers based on Netscape's plugin model like Mozilla Firefox.

It is for this reason that Mozilla Firefox 3 and Internet Explorer 7 have restricted what objects can be installed and run to objects that are trusted and make it hard for users to make exceptions as without knowing if the object can be trusted, it needs to assume it cannot be trusted by default.

Internet Explorer 8 RC1 takes this even further by not allowing even trusted objects like Flash to run on untrusted web sites without asking the user.
Popular sites like msn.com will be trusted sites by default.

Indeed, testing things is a good way to figure out what works.
Also, The Geek could just write code that will recognize objects which are loading Videos from trusted sites like Vimeo or YouTube which some forums have done but it is extra work that is not worth it when like you said, a link suffices.