It should be a choice, stay as gateway and get stronger units or faster build time. Go to warpgate make the units weaker or take longer whatever. The game would have a great new layer if players had to strategically choose when to do warpgate and when to stay gateway. Warpgate should be a late game tech essentially used as harass. At the least units should warp in with no shield and essentially make it so they used their shield energy up warping in.
They just want to be able to say all 3 races have unique production, but if that is the case then why not have carriers and probes warp in? This one design has held the game back so much as it relates to Protoss balance even things like warp in with storm etc.
They aren't changing it though.