My experience with keyboard arrangers is this:
Keyboard arrangers (Yamaha, Korg, etc.) usually have from 2 to 8 measures of music that play over and over and over again. Often very good styles, but no "intelligence"
BiaB styles can have hundreds of patterns ranging from 2 beats to two measures that can be assigned to be played in appropriate musical situations. In addition, the style author can write more than one pattern for each musical situation, and assign probability numbers for them, so the ones with the most personality appear less frequently. The result is less repetition and more musical appropriateness to the patterns (since you enter the chords before clicking play, BiaB knows what chord comes next and can choose the patterns 'intelligently')
Keyboard arrangers generally have 2 rolls, BiaB styles can have more.
The keyboards usually have better intros and endings, and often more than 5 instruments.
Personally, I think the output of BiaB is both much less repetitive and much more musical.
Insights and incites by Notes
Brand new 2012.5 updates from Norton Music:
- 2 new style disks for Band-in-a-Box
- 2 new free (with a purchase) fancy intro/ending disks for Real Band and other DAW's
- The Ultimate Gospel Fake Disk
- The Real Rock Fake Disk (plenty of classic rock in this one)
- The Beatles Fake Disk
- And an updated Christmas Fake Disk
Hundreds of Free .sgu and .mp3 demos for the above at: http://www.nortonmusic.com