No, in Fusion you start with the Fusion suit. I believe the whole thing was that the Power Suit protects Samus from any ill effects from her weapons, and the reason she can't use the Ice Beam until she gets it is because she doesn't have it to protect her metroid-fused body from the ice.
The appearence of the suit doesn't change when you go from Varia to Gravity either. The point is the name of that form of the suit, not weather or not it is the same suit. Of course it's the same suit, all the other "suits" are just add-ons.
In Metroid 5, would Samus have the Fusion suit or her original Power Suit? I'd think Fusion Suit, as that's what she has even after absorbing the SA-X.
The way I always viewd the first suit was, like in all the other games except 1 & Echoes. She starts with her Varia suit, something happens she switches back to her orginal Chozo given suit which I have always hear to be called the Power Suit. But in Fusion instead of going from Varia to the Chozo Power Suit she goes from Varia to her Power Suit but it now has the Fusion look due to surgically removing the armor. So the last suit couldn't be her Power Suit since that was the first Fusion Suit we got to play her in.
And Knight, there's no Phazon-resisting capacity in the SA-X's suit. The SA-X has Power and Varia. Gravity didn't carry over from Super Metroid, and Samus lost Phazon at the end of Metroid Prime. The only components the SA-X had that Samus didn't when she absorbed it were the Ice Beam and the Power Suit.
It was the Varia suit, unti lshe got infected by X. They performed surgery on her, trying to get the suit off so that could tryu and treat her. When parts were removed, she looked horribly disfigured. Well, the suit looked horribly disfigured, we saw at the end Samus herself looked okay... But anyways, when they injected her with the Metroid vaccine, it began to mutate the suit in physical ways. Probably because the suit was made by Chozo, Metroids made by Chozo... Some weird reaction happened, yadda yadda yadda... When she woke up, the end result looked like the blue Fusion suit.
Personally, I've never thought that any X took Samus' abilities. Any abilities that Samus didn't have were taken by the surgery. And since the X that came from the suit parts infected Samus at full strength, they became a full-strength SA-X.
The Varia Suit was originally to be downloaded, but the Core X absorbed that data. Then the Gravity Suit was taken from the Nightmare Core X. So the way I look at it, there weren't really suits that you got. Merely suit effects that you got. Remember when you absorbed a suit, the message said "Varia/Gravity suit effect recovered."
So when the SA-X was absorbed, it abolished the Metroid DNA coursing in Samus which allowed her to host the Ice Beam. The suit never changed because only the effects were absorbed.
The effects absorbed from the SA-X was the color, the destruction of the Metroid DNA in her, and thus, the ability to host the Ice Beam again.
Therefore, there was never anything but the Fusion Suit. Just suit effects that came with colors.
If she lost the Metroid vaccine, the SA-X she just absorbed would have killed her. Remember, the Metroids are the natural enemies of the X, not the other way around. I'm convinced that she merely absorbed the Ice Beam and the capacity to use the Ice Beam without it freezing her own body.
LifeMega was talking about the lack of a physical structure change in the suit, apart from the color. Which is exactly what Starman said in the post LifeMega was answering.
The first 3 suits (fusion, varia and gravity) are all rather the same, but with some extra effects. They look exactly the same, except for colors, as starman pointed out. The last suit you get really does look different, atleast ingame. So I guess it's the original suit, before the operation, with some slight modification thanks to the X infection, the metroid vaccine, and the fact that she doesn't have the same body-suit anymore (since the surgury altered it.)
Well, SABER, the X that infected her suit split off with asexual division, throwing out at least nine more SA-Xes. Does it really matter whether it was the original if they all have the same DNA?
By the way, why is it that you obtain ice beam from the fully powered suit and not the hyper beam? I mean besides the fact that it was weaker than the other beams. >_>