Assuming this is true, then these stats are heavily influenced by the first knockout rounds, when the group winners play the first game away.
In the later stages it doesn't make much difference. For example, in the last 5 seasons we have this case:
2010
Bayern-Lyon 1:0 - 3:0
Inter-Barcelona 3-1 - 0:1
2011
Schalke-Manchester United 0:2 - 1:4
Real Madrid - Barcelona 0:2 - 1:1
2012
Bayern-Real Madrid 2:1 - 1:2 (3:1 pen)
Chelsea-Barcelona 1:0 - 2:2
2013
Bayern-Barcelona 4:0 - 3:0
Dortmund-Real Madrid 4:1 - 0:2
2014
Real Madrid - Bayern 1:0 -4:0
Atletico M. - Chelsea 0:0 - 3:1
As you can see, 8 of the last 10 CL finalists played the first leg in the semis at home. Even those 2 finalists who plyed the first semifinal away, basically won the encounter in the first leg already.