Range Balls

There seems to be a concensus that range balls are shorter than "real" balls, but does anyone have any info on by how much? Or even if its true?

In previous "feel v distance" discussions on here its been suggested that the difference between the longest and shortest ball is only 10 - 20 yards depending on club and swing speed - is it much the same between range and real?

I think to work out your distances you need to hit 30 or so balls discarding the 10 longest and 10 shortest and looking at the average of the rest.

Unfortunately the only place I can do that is at the range so knowing that I can expect say 10% more could be useful - assuming I was swinging consistently in the first place

My question is why should range balls go less distance?

Because they're worn out?

Because they're inferior balls?

Because range balls are designed to go less distance?

What would be the point?

Here's what "about.com says:

“Range Ball”
Glossary
Definition: 1. A golf ball specifically manufactured for use on a driving range, or used balls that in use at a driving range. Golf balls made for driving ranges feature very hard covers so they won't be easily cut or damaged. Range balls often have a black or red stripe going around them and so are easily identified.
2. A derogatory reference to a golf ball that is not performing as hoped (usually at the fault of the person hitting it). One partner to another, "That shot was ugly. Are you using a range ball?"

I had the same question when I started playing a few years ago. Frank Thomas, Chief Technical Director for Golf Digest wrote in April 2005, "They are the same in all respects to the ones you can buy at the golf shop, other than the stamp of the word "PRACTICE." Like most X'd out balls, these would confomr to the Rules of Golf. However, in competition, the committee might stipulate that balls must be on the USGA's list of conforming balls, and therefore, balls with "Practice" stamped on the side would be disallowed. Some touring pro's insist that the practice balls they use on the range be the same brand as the type as those they use in competition. This is a good indication of the quality of these practice balls." (Amiste)