This is the Chuck Schumer show.
AFAIK, admin. officials not subject to Senate confirmation (Nat. Sec. Advisor, WH Counsel, press secretary, political advisors, etc.) cannot be compelled to testify before Congress unless a crime is involved or alleged. You'll recall that when Rice was still Nat. Sec. Advisor, there was no real serious talk of subpoenaing her, because Dems did not want to set a precedent that could later be used against them when they have the WH again. And I think any president is entitled to candid and confidential advice from his advisors. If every word could be subject to a televised Senate hearing, then no one would ever tell the boss what they really think.
Cabinet secretaries, who are subject to Senate confirmation, have to testify on the Hill all the time. And if the hearing is not televised, they are not usually put under oath. The under oath thing is purely for the tv cameras and means absolutely nothing, since lying to Congress equals perjury whether under oath or not.
Since no crime could possibly have occured here, as the president can fire US attys. for any reason, there is no way Rove or Miers should have to testify. I wouldn't even let them be interviewed without some big concessions on other issues from Congressional Dems. Why should Bush appease them? He has the law on his side and has no reason to give them what they want.