It is uniform and we do explain the scale chosen, which keeps everything relative to each other regarding weapon ranges, movement, etc.. The city terrain I did for Polyversal's videos is scaled per Google maps satellite view... but at that scale, 1/300, a 4' square area is only several city blocks... not an entire city... so most every miniatures game out there has a compressed horizontal scale except the more skirmish-type games which may be true. Theminiaturespage and other online sites have articles devoted to this, and in most rules sets, scale choices such as this are discussed (or should be) in the rules.
As an example... a typical firing range for a WWII tank may be up to 1000 yards or more... artillery... from miles away... but to cover those larger distances in an exact horizontal representation of even 6mm scale, you'd need a gymnasium... so... Most of the games I've played represent height to a scale so the figures look right to each other... but horizontally, those scales are compressed to fit the game in a typical gaming space.
Example-- 1000 yards firing range = roughly 914 meters * 1/300 = roughly 3 meters or 9' of gaming space to represent that firing range, which is a bit impractical.
Here's a discussion board devoted to scale if you're interested:
http://theminiaturespage.com/boards/topics.mv?id=161There are a lot of discussions on the topic. We're not saying Polyversal is correct, but, it is consistent and works well to handle a battle over a large area in a relatively small gaming space.