An average of 45 in the 80's is actually very good, an average of 45 would put you in 15th place for the decade. In the 2000's Mike Hussey's was in 15th position. Also there where some terrible wickets in the 80's where batting was a lottery, that would explain some the starts that where not converted into hundreds.
80's batting averages
2000's batting averages
Richards was one of only 6 batsmen to score 1000 run at a better average greater than 50 in the 80's.
My memories of Melbourne wickets in the 80's was they where very wet on day 1 with the ball swing around all over the place. Day 5 even often worse with bouncers coming through at ankle height.
All the Australian wickets (bar possible Adelaide) where bad for batting. Even though wickets in a Australia where in poor condition, Batting averages in Australia where higher than most countries.
Personally I think some of 80's bowlers get over-rated and batsmen get under-rated.