James,
Yes, it does matter. Of course you can mark out the correct size (my group routinely does this playing SAGA, because no one had a table that is only 4'x3'). The issue though is that unless you see this thread, you won't KNOW to use the smaller area. As a result (like the posters above, you will set up the scenario over a 6' x 4' space, thus throwing off the intended distances, ratio of terrain to empty space, etc.
Also, when we say "table" in a context like this, we really mean "playing area."
Clearly someone (probably whoever prepared the English translation) was too lazy to look up the correct conversion of 120cm x 90cm to Imperial. Or maybe they just asked the author what size table, were told "standard size," and assumed that meant the U.S./U.K standard of 6'x4', when what was meant was the Studio Tomahawk standard....