Or perhaps they didn't.

I remember that the original ruling that the Trap/Spell mechanic was only valid for the YuGiOh scenario was made as a post on the forums. Has there been any official statement on WizKids site or on the WizKids rules forums confirming this?

It would be nice if there was an official statement or errata to the rules documentation providing the exception. As it stands the only ruling we have on it was made in a post in the General Discussion forum here.

It doesn't get any more official than the actual rules document included with the YGO starter. That document describes the YGO scenario and is only place where the rules for traps and spells are defined. Since they are not defined outside of that scenario that is the only scenario for which they are allowed.

EDIT: Don't get me wrong, I would love to see them be allowed outside of the scenario. They can be powerful, but I don't think that they are game-breaking.
But the bottom line is that they're no different than lots of other things which were specific to scenarios, such as with the old colossal, like Galactus or Dr. Manhattan.

Ahh, I had always assumed that the rules given on the character card for Trap/Spells were sufficiently explained on them to play them in Golden Age events. I never purchased the Yugioh starter set and assumed it was just like any other Golden Age only set such as Lord of the Rings or Star Trek. If the only place that the full rules for Trap/Spells are fully defined is in the scenario I would have hoped that WizKids would have published a copy to their website.

Thanks for your help.

There was an official ruling from WKs saying Spells/Traps were only allowed in the YGO scenarios. I'm not sure if its still up on the WIN.

Sorry that my respond is late..But THANK you for posting..And i WILL ask about Judge how to use Magic/Traps at games..It is really hard to play "YGO Themed" game since i am the only one who has a lot of YGO clixes..But Untill there is a Golden Age game i hold off Playing a YGo Team..I also ned to fix some of my YGO Teams and make some more so while i am working them out i have a lot of OTHER teams to use.

In response to the original post, it would seem like your build is legal. I don't have the rules sheet in front of me to confirm, but if it's 1 spell/trap per 100 points, then yes, 4 would conform to this. On keywords, it also seems clear the special keywords introduced here are all named. Take Master Kyonshee, for example.

Master Kyonshee lists 2 new keywords while also sporting the generic "martial artist" keyword. As previously stated, the font (at least from what I see in the Units section) seems to indicate only "martial artist" is generic here. It doesn't really get clearer than that.
As for legality of YGO outside of itself, I can see why it's restrictive, albeit just from a casual player's perspective. Although spells/traps are specifically only for YGO figures, I imagine they're done this way so as not to compound with feats by making only YGO figures usable there. It came to me when I saw you're including a Thug, and I thought "why use a Thug instead of a feat or resource?"

On a more sentimental note, I'm all for keeping YGO HC alive. I absolutely love the YGO license. I just wish they didn't restrict themselves to a bunch of unrecognizable, old characters. The elemental heroes alone would stand to make a solid set, despite the obviously hilarious situation of including characters that are parodies of superheroes in an offshoot branch of a game originally for superheroes in the first place.

The YGO scenario can be quite fun, but you can play it with any characters.

Just watch out for someone who stumbles upon starting off with two Grundys.