This is related to HTML itself, and not the board software. IPB has the same "problem", too, as you can see by
this post (need to log in to view it, since it's in Forum of Randomnity). I didn't count the spaces I put, but I used a whole bunch in between each word, and there still is just one.
Setting the board to allow HTML won't work, because the board software will escape text/convert it to HTML codes ( like <, >, and ), for security reasons, perhaps. The only way you could get multiple spaces to show in a sentence is by using the Code tag, like below:
This sentence has 10 spaces between each word.
I don't see the need to have the capability to put more than one space between each word, but if you do need it, you can use the Code tag. Or, I can make a preformatted text BBCode that will work pretty much the same.