this is what wiki says about the "soprano assoluta" :
"Soprano sfogato ("Vented" soprano) is a term which, in the art of singing, designates a contralto or mezzo-soprano who is capable-by sheer industry or natural talent-of extending their upper range and being able to encompass the coloratura soprano tessitura. It is sometimes called soprano assoluta."
I find those videos ridiculous, because I don't think that a singer should be judged just by technical abilities (as I don't think that an actor/actress should be judged for his or her beauty), but reading this it seems that even that "assoluta" is just a definition of range.
"Coloratura" for what I know is just a definition of the agility of the soprano in singing fast passages, so it does not have anything to do with being trained or not.
I've heard trained singers with terrible voices and untrained singers who are able to do virtuosistic passages.
So my "problem" with those videos is the idea that the value of a singer has to be found in their ability to hit high notes or do fast melismatic passages and stuff like that.
I mean, Maria Bethania has probably the range of a contralto and I've never heard her doing any virtuosistic thing, but she is incredibly better in my opinon than those sopranos (assoluta or not) like Mariah Carey or Whitney Houston.
I have a thread about the Assoluta and how it only should be referred to OPERATIC artists. Here's that link and maybe you can you can see for yourself the description of that type of voice in Opera. http://www.talkclassical.com/44122-soprano-assoluta-its-place-5.html
Second, there's a huge disparity in given certain singers certain terms like "Soprano" or "Mezzo-Soprano" in Pop Singing. When we give those terms to an Operatic singer, it's usually during their years as student in high school or even College (for those who still feel they are changing, vocally speaking.) For example like Joyce DiDonatto have stated several times in her masterclasses it took her a while before she truly knew what she was and even then it frightens her because of how big her range is and how versatile she can be.
Whitney Houston started off with a very beautiful instrument, no doubt about it but even in her "prime", she was a pure Mezzo-Soprano who was extremely gifted with an upper register "belt" (something Operatic artists don't use because it's not needed in Opera). She could've expanded her range but she didn't feel the need to because she was one of those type of rare singers who believed the pure essence of her workload and the beauty of instrument would get her far and not some gimmick like having 5+ octaves (I'm looking at you Mariah, Georgia Brown, etc.). Now don't get me wrong there are some extreme cases of pop singers in the 70's (Minnie Ripperton) who actually had a GREAT 4-5+ octave range and they used it sublimely and it showcased their music and vast versatility on so many levels, but again in Opera, we don't care about the ranges as much as the characteristics of what your voice type has.
Not to get off topic here, Whitney had no lower register in her early days -- this is a fact. It actually took her a decade before she found that area and as performances from her 1993 New York City concert to the 1994 New York Concert, she would often use a lot of chest in that area. The fact that by 1990, the voice was no longer as sweet nor was it comfortable on the top as it had been for her first 3-5 years, proved to be almost disastrous for her. She would use melissmas to hide the fact that she was losing it on the top (and it's important to note, she was always sick from 1990-1991, with 1992 being the exception for if you look at her performance at the '92 AMA awards.)
Here's a video comparison of her performing "Greatest Love of All" from 1989 (late '89-early '90 recording) to 1992. (The '89-'90 recording is a LIVE recording because the live recording video was taken down, Arista used it for their DVD)
And now, the 1992 live recording as a tribute to Muhammed Ali: