All of DL regional jets (CRJ-200/700/900, EMB-170/175) are 2x2 in coach. AA has Piedmont ERJ-145's with 1x2 seating on FAY-CLT, but DL no longer has any such aircraft. Weight and balance issues are not uncommon on the regional aircraft. They base the weight savings on averages and have no clue how much each passenger actually weighs. No, you are not due IDB compensation as you did not have a confirmed booking on the flight. Also, if you were on a CRJ-200 (which appears to be case as all the regional flights on this route are currently Skywest CRJ-200's), aircraft 60 seats or under are exempted from DOT IDB rules if denied due to weight/balance issues (which should tell you that such issues are not uncommon for these aircraft).