You're right; I stayed over 90 days, so I had to, but I didn't realize that was the rule -- I thought it was for anybody and everybody, basically. Full text from DoS:

RUSSIA - *Passport and visa required. Tourist visa, valid for 30 days, requires 1 application form, 1 photo, confirmation and voucher from travel agency and/or hotel in Russia, cover letter from travel agency, and processing fee. Business visa requires 1 application, 1 photo, cover letter from your company, and letter of an official invitation from an authorized Russian counterpart and visa-processing fee. Single-entry visa for business/tourist visas are $100 for not less than 6 days, $150 for not less than 3 working days, $200 for next business day, and $300 for same day processing fees. Multiple-entry business visa (needs confirmation through the Russian MFA) processing fee $100 for not less than 6 days, $200 for not less than 3 working days, $250 for next business day, and $350 for same day processing fees. Fees must be paid by money order or cashier's check only. Provide SASE for return of passport by mail. HIV test certificate required for anyone staying over 3 months. For additional information, contact the Consular Section of the Embassy of Russia, 2641Tunlaw Road, NW, Washington, DC 20007 (202/939-8907 or 891 or the nearest Consulate General: NY (212/348-0926, 0955, 0626), CA (415/928-687, or WA (206/728-1910). Internet: www.russianembassy.org