There is a time and place for everything. Vocal acrobatics were around long before Holiday or Houston (both who were brought up in the type of churches where such singing is greatly appreciated and respected and in many ways is described as giving God "everything that you've got") In various genres, jazz, gospel, r&b, soul, even opera vocal decorations are quite popular - so I wouldn't blame Holiday or Houston for something that is much bigger than either of them.
And frankly, I'd hardly call what those two ladies are known for "Idol" style singing. While Ms Holiday certain has become almost a caricature of herself today, when she was on top (a la Dreamgirls) - I think it was impossible to not feel every ounce of her emotion whenever she sang. THAT is why audiences responded to her. She was giving the material everything she had - blood, sweat, and tears - night after night. Even though she wasn't the best actress, you felt every minute of her performance - and for that she was rightfully applauded.
The "Idol" kids today don't compare. I do agree that many concern themselves with showing off and forget the connection to the text. Sad to say, there are many voice teachers who encourage this - "add a riff there" mentality. But there is a time and place for everything...
In a show like DREAMGIRLS, the audience is applauding for yes Vocal Acrobatics but they are also (in a good production) verbally reacting because they feel connected to what the actors are singing. It is VERY appropriate in the genre. If you don't like the genre, don't attend the show.
I apologize for the length of this reponse. All of that to say, yes, while Marty does have a gorgeous voice...he DOES fall into the "Idol" style of singing (as you call it) more often then not - making it all about the new riff and throwing his head back to make sure you know he's got that high note. Marty doesn't have to do all of that...it hardly sounds natural on him for the most part.
