It's possible, but Google is almost everywhere and people have yet to get used to using Siri or Vlingo on a regular basis.
I think Schmidt may be intentionally up-playing Siri, reverse psychology maybe? ....I could be wrong, but Google is just so ingrained into everyone's daily lives with searching, everyone says "Google it" or simply searches for something in their search bars and chances are it's Google.
Along with Gmail ads, I don't think they'll be hurting too badly because of Siri.
Apple doesn't have free email accounts to the general public do they? Unless you use your MobileMe, now iCloud, which is strictly for people who own Apple products.
Either way, if Siri is a threat, Google will find another way to blanket people with ads, and vice-versa.
(off on a tangent, but) ... I installed Vlingo, but I still find it faster to text or call someone with a quick Swype or touch of a direct dial shortcut on my screen.
Maybe in a few years when Siri, Vlingo and other virtual assistants are more intuitive, quicker and what not, maybe then speaking to your phone will be great, but for now, they're okay, not great.