"Microsoft created what amounts to a third tier that was never meaningfully disclosed. Solely for the duration of the 'Vista Capable' program in the ten months preceding the launch of Vista, OEMs could certify a PC as 'Vista Capable' even if it did not support the Windows Display Driver Model or WDDM --- one of the requirements for a Vista Basic logo at the time of launch," plaintiffs' lawyers wrote in a motion supporting their request for summary judgment on the WDDM issue. (18-page PDF)

The motion was filed Oct. 17, but unsealed only today.

The plaintiffs argue that the three tiers were the Premium editions of Vista, which could run the Aero interface, featuring a translucent glass appearance; the Basic edition, which could not run Aero, but did support other WDDM-dependent features, such as "enhanced graphics stability [and] multi-application performance"; and a Basic edition, which could not run Aero and did not support the other WDDM features.

"This stripped-down version of 'Vista' is not even 'Vista Basic' as Microsoft itself defined it, to say nothing of whether it could fairly be characterized as 'Vista,'" plaintiffs' lawyers wrote.

Microsoft did not adequately explain to PC purchasers the significance of WDDM and this "third tier," they argued. Only two public information sources cited in the case record, they noted, distinguished between Basic with WDDM tier Basic without WDDM, "but they never explain that the 'Vista Basic' to which 'Capable' PC buyers could upgrade would actually deliver less than the 'Vista Basic' they would have received if they had bought after launch," plaintiffs' lawyers wrote.

Attacking Microsoft's disclaimer that "Not all Windows Vista features are available for use on all Windows Vista Capable PCs," plaintiffs argued that it "does not convey the reality of dropping the WDDM requirement. ... [It] does not disclose the functionality gap between Vista 'Basic' without WDDM and Vista 'Basic' with WDDM.

"Rather it promises that 'All' PCs that are 'Vista Capable' 'will run' the 'core experiences' 'such as' 'innovations in ... security, and reliability.' Those within Microsoft who understood what really was going on knew that non-WDDM PCs would not live up to that promise."

The plaintiffs pointed to testimony from Microsoft's Megan Wallent, who said that some improvements in security, reliability and stability involve or require a graphics processor that supports WDDM.

The plaintiffs are asking U.S. District Court Judge Marsha Pechman to rule that branding of PCs that "would never meet even Microsoft's own requirements for 'Vista' " as "Vista Capable" was unfair and deceptive, and thus violated the Washington Consumer Protection Act.

Here's Microsoft's opposition to the plaintiffs' motion for summary judgment on the issue: 28-page PDF.

For more background on the case, see these earlier stories.