Beware of prosecutors: they don't like to lose. Scooter Libby today became at least the third high-profile person in recent memory to be successfully prosecuted for lying about something that wasn't a crime.
Bill Clinton, Martha Stewart, and Scooter Libby were all prosecuted for perjury charges that were really tangential to the original case. In all three cases, prosecutors, hot to not be left empty-handed when pursuing a high-profile target, fell back on prosecuting perjury charges related to non-crimes once their core case fell apart. Only Bill Clinton escaped jail, escaping with what was effectively jury nullification -- no one seems to deny he was guilty of perjury, but his jury (the Senate) couldn't bring itself to impose a ridiculously harsh penalty for lying about something entirely unrelated to any crime and which in a reasonable world would not even have been allowable questioning under oath.