The Dutch take on Wales in Amsterdam on Wednesday in their final friendly before their FIFA World Cup opener against Spain on June 13.
However, Real Madrid forward Bale will not play due to a nagging leg injury and Arsenal midfielder Ramsey has been rested.
Van Gaal, who will begin his tenure as Manchester United manager after the World Cup in Brazil, revealed his disappointment at their withdrawals.
"I have said to my board (the Dutch FA) that they had to insist on playing against Gareth Bale and Ramsey, but this can happen in football," he said.
"I don't know why, whether it is injury or holidays. When it is a holiday I am a little bit disappointed, but I can understand it because Bale has a difficult, but also impressive, season under his belt.
"It's better that we have the best team of Wales because we need resistance.
"I think Wales without these players are weaker, but I have seen Wales play, against Iceland and Finland, and I like the way that they play.
"It's not a bad team, but with Bale it is always better, with Ramsey also."
The Netherlands take on world champions Spain in Salvador in what will be a repeat of the 2010 World Cup final.
Get the best features, fun and footballing frolics straight to your inbox every week.
Thank you for signing up to Four Four Two. You will receive a verification email shortly.
There was a problem. Please refresh the page and try again.