Clear Channel is beefing up the lineup on its 910 AM frequency, first by hiring fired KGO hosts Len Tillem and Gene Burns, and now by adding Rush Limbaugh. The new lineup starts Jan. 3. Limbaugh’s move was revealed publicly in a tweet by 910 morning hosts Armstrong & Getty. There are two schools of thought about why Limbaugh is changing stations. One is that his show is expensive and KSFO’s owner, Cumulus Media, is cutting costs. That’s why they laid off most of the talk hosts at KGO and replaced them with less expensive news staffers. Another theory is...