The additions have helped United to reach the UEFA Champions League final after losing to Milan in the semi-finals of the competition 12 months ago.
"If you look at Sir Alex's 21-and-a-half years here, a feature is that he has not been afraid to changes his teams," Gill told Sky Sports News.
"We had a very successful season last year, but he, Carlos (Queiroz) and the chief scouts and everyone analysed it and said, 'where did we fall short' and we said we've got to continue to invest.
"Like any business or any club, you've got to invest when you're at the top and that's what we did. It's worked out very well."
Gill also insists that Ferguson's transfer plans for this season had not been solely influenced by the 3-0 defeat in the second leg of the Champions League semi-final with Milan.
He added: "We invested heavily in some young players, and experienced players like Owen as well, but the decisions weren't made on that one game.
"You can always lose a cup game for whatever reason - the other team were better on the day - but we looked at it with a view to the long term.
"What's happening with the team and the age profile of the team in certain areas. This is what we need to do to ensure that there's a smooth transition from one team to another.
"All the media and all you pundits talk about the various teams Alex has put together and that's been a key strength of his over the years - to recognise where he needs to change things and, obviously, he's not afraid to do so."
