Would you like cherry or grape Koolaid?
Seriously, it's pretty close to a Blade 98. The beam layout, etc. The only thing that's different from the looks is the string pattern and it's tightness in the center.
Generally speaking, if the frame was a Blade 98 custom drilled, Wilson would be well within truth to say the racquet was a custom frame build specifically for him and not available in stores... because it's not due to the different drilling pattern on it.
Besides, what sounds better? "We picked something off the shelf and changed a few small things and handed it to him." or "We custom build a racquet in our test lab specifically for him."
Generally speaking, when you're developing a prototype for someone like this and you have something in your normal list of products that already fits 80% of the needs, you start with that as your base. 98", throat and beam design like a Blade 98... go with that and change a few things on it specific to his needs.
Bottom line, is it exactly a retail Blade 98. No, of course not. But it's not a one-off custom job from the mold to the paint either.