It's not that Standard Rooms at Poly are specifically excluded from discount, but in general, it is difficult to find availability for a Poly Standard to receive a discount. They book up without a Disney discount, so Disney usually are seen discounting Lagoon and Theme Park rooms at Poly, rather than Standards.
I would expect, also, to see Poly Studio Villas join the "no villas on the monorail line" general exclusion of discount once Poly finishes its last unit declaration to DVC/sells out. Copper Creek will discount for a while, as Disney own 75% of the units there right now.