[JCP-YGO] VWXYZ & related fusion monsters question

[UDEbot]

VWXYZ & related fusion monsters question
from UDE's Judge Certification Program (YGO)

I was looking at the rulings for the XYZ FUSION MONSTERS and VWXYZ-DRAGON CATAPULT CANNON. Their summoning requirements are the same, yet VWXYZ can be Special Summoned from the Graveyard and the XYZ monsters cannot. The rulings are from the UDE website here. I do not see anything that would allow one monster to be Special Summoned and not the other. Could you please explain why the rulings are like this?

VWXYZ-DRAGON CATAPULT CANNON
Once properly Summoned by the method written in the text this card canbe Special Summoned from the Graveyard with effects like “Call of theHaunted” or “Re-Fusion”.

XYZ FUSION MONSTERS
The following rules apply to "XYZ-Dragon Cannon", "YZ-Tank Dragon", "XY-Dragon Cannon", and "XZ-Tank Cannon".
These monsters cannot be Special Summoned from the Fusion Deck exceptby the method described in their text. So they cannot be SpecialSummoned by the effect of "Magical Scientist" or "Summoner ofIllusions". They cannot be Special Summoned from the Graveyard evenafter they have been Special Summoned by the method described in theirtexts.


http://entertainment.upperdeck.com/COMMUNITY/forums/thread/1026329.aspx

 

[harvey locust]

read your card text....

xyz says
<TABLE class=card_text><TBODY><TR><TD>Text</TD></TR><TR><TD>"X-Head Cannon" + "Y-Dragon Head" + "Z-Metal Tank"
This card can only be Special Summoned from your Fusion Deck by removing from play the above cards on your side of the field. (You do not use "Polymerization"). [yh]This card cannot be Special Summoned from the Graveyard.[/yh] By discarding 1 card from your hand, destroy 1 card on your opponent's side of the field.
</TD></TR></TBODY></TABLE>

vwxyz says
<TABLE class=card_text><TBODY><TR><TD>Text</TD></TR><TR><TD>"VW-Tiger Catapult" + "XYZ-Dragon Cannon"
This card can only be Special Summoned from your Fusion Deck by removing from play the above cards you control. (You do not use "Polymerization"). Once per turn, remove from play 1 card your opponent controls. When this card attacks, you can change the battle position of the attack target. (Flip Effects are not activated at this time.)
</TD></TR></TBODY></TABLE>