Why convert a VCD(DAT) to a mpg

[ColtWalker]

I just read the - How to convert a VCD(DAT) to a mpg - guide on this web site.
http://www.vcdhelp.com/convertdat.htm
One thing the guide fails to mention is this, just what exactly is the difference between a fully compliant VCD mpeg file and the .dat file on an actual VCD disc? This leads me into the following two questions:

1.) Why not just rename the .dat file to .mpg?
2.) Is there any quality loss in converting the .dat file to a .mpg file of VCD specs using the software mentioned in the guide?

Thus far I have archived my vcd compliant mpg files to cd using VCD format, resulting in the .dat file. I assumed that this file was basically the same as a mpg file. The existance of the guide suggests that I am wrong and that there is a difference between the .dat file on a vcd and an mpg file of vcd specifications. Which leads me back to my primary questions, what is the difference and why would I want to convert my .dat file back to .mpg with software as opposed to just changing the file extension to .mpg?

Thank you

[Stansell]

There is a difference. I'm not sure exactly what it is, but there is a difference.

Some programs can't handle a .dat renamed to .mpg, while others can.