That change to the profile table was made sometime in the past (I want to say 4.6.2 or thereabouts).  I remember when I first upgraded to the version where that change was made and saw all sorts of code stop working (or rather, just not pull the data I was after).  It sucked (I had written several pretty comprehensive modules that relied on some hidden profile properites). 

At any rate, I believe that you cannot change that behavior at this point and unfortunately will have to change your modules that reference the profile properties with spaces to pull them with an underscore.  On that note, ProfileProperties now have the ability to be "Localized" so you could effectively still display them with spaces in their names but behind the scenes they will have an underscore where you had spaces.  You go into the same spot you defined them to set up the localization text.

I think the motivating factor to move to underscores instead of spaces was to ensure "compatibilty".  It is considered by some circles that having spaces in a database key to be bad practice.  The profile properties use an autogenerated INT as their key but all the lookups are done against the name (so it can be considered a key).