Inconsistent behavior while adding url in embed content on page

Description:
1. Login as an instructor, select a course site and then click on lessons
2. In lessons click on add content --> click on embed content on page
3. Add a URL(example www.google.com) in space provided in "add a URL or embed code" and then click save.

Problem:
The behavior is inconsistent while adding URL, i.e., it is displayed as an image for some URL'S and displayed as a link for others, for example it works for YouTube and doesn't work for Facebook, google etc
1. Doesn't work for Facebook, google
http://www.evernote.com/shard/s562/sh/064eed54-d985-4aca-9715-2c674a18bcfb/ed9f5f4dc2125b5079e9a9e29968fb54

2. Works for YouTube
http://www.evernote.com/shard/s562/sh/75955df4-23b7-4f3f-904a-cbc2c7704451/d700855fb4d92bc0dcc22407c851aefc