I just thought that I cannot find any reason (security? what kind of? may be uselessness?) you can include any image into your HTML page (from any foreign website and the owner of it can delete/alter it later) with a simple <img src=...> tag while plain text embedding is a very tricky task.
The only solution of embedding text into HTML page on client side I know is <script src=...> with document.write inside.
Do you know why text embedding wasn't included into HTML standard with a simple tag?