Out of curiosity, I just looked in my manual for Cubase LE and it says the MP3 encoder is included with upgrading to full a version.
It's simply a matter of cutting costs. They don't include software they do not own or have licensing agreements with because that costs money.
To me it makes no difference as converting to MP3 is a post Mastering process done with mastering software. I only ask Sonar to produce the highest quality wave file I can get my hands on. I don't expect it to make a you-tube either.

It is a matter of cutting your cost. You so rightly observe, some people don't need or want an mp3 encoder in their DAW. CW does not force you to buy it but they do provide the ability to try before you buy. With the full version of Cubase you pay for it whether you want it or not.

BTW the links in http://forum.cakewalk.com/fb.ashx?m=1774575 are bad. It should would be nice if someone could re-post the files.