It is true and it isn't!
The bezier masking tools within P and and Crop are NOT available in Movie Studio/MS Platinum. However there are still plenty of masking capabilities. For example create a mask in PhotoShop or whatever - white being the bits you want visible.
For a simple example, suppose you have Video events A&B and you want video A to appear as a circle in the middle of video B.
Place Video B on the "Video track" and video A on the "Overlay" track.
Now place your still image (white circle on a black background) on the Text Track
Now two bits of magic..
Change the compositing mode of the text track (the circle) to Multiply (Mask)
You should now see Video A as a circle with nothing (ie black) surrounding it.
Now make the "Overlay Track" a child of the text track ad Video B will surround the circle.
You could then use track motion to move the overlayed mask and substitute different shaped masks as appropriate.
The limitation is that you can't change the shape of the mask using keyframes.
Yes, Vegas Pro is much more expensive, but then it has more advance features such as Bezier Masks. Movie Studio/Platinum represents excellent value for money and give you everything you're likely to need for 90% of the time. And most things can be worked round with a little imagination.