It's answered in some of the 4 hour conversations
Including some of the ones I already recorded and have yet to release (with Sierra composers Neal Grandstaff and Mark Seibert)
The short answer is: The composers composed for the Roland and then "downgraded" them for Adlib and downgraded again for the PC speaker.
A lot of the times I prefer the Adlib / Soundblaster versions because that's how I remember them from my childhood.