Interesting points. I hope others weigh in.
First off, I wouldn't call KIRO, even in its mid-late 70's confiuration, 'all news.' The old mid-day show (which I miss) would break format for breaking news on a dime, and featured a magazine-style short interview format (as opposed to caller driven talk shows). But it was still a news/talk hybrid.
KING tried a horrible cheap kind of all news (lead by a horrible GM, but that's a personal history bias) in late 1982, with the audio of CNN Headline News as its bedrock programming. Don't get me started.
KOMO's take on the basic WCBS format isn't the best in the world, but it fulfills my definition of an all-news station -- even one that does play-by-play: when the team or team-related programing isn't on, the news is on. Simple as that.
Yes, the success of the news programming begats the issue of games interrupting the news. In Chicago a few years back, WBBM took a lot of heat when it didn't interrupt a Bears game when a major, killer storm came through town (way beyond the usual storms that hit Chicago).
WCBS has the same issue with the Yankees -- although WINS, its competitor, is also owned by CBS. In LA, I believe KFWB does a lot of sports (including Monday Night Footbal in PM drive during the fall), but KNX takes up the slack.
Every other town with an true all-news station (and there are darn few) probably puts up with the same situation.
On the FM news subject, a thought or two: Here in DC, WTOP has done very, very well moving its true all-news format to FM. But the AM was the lamest 50k station on the east coast -- audible in Rio de Janero but not on 14th St. at night. The FM puts the station into offices and high-rise condos where it couldn't be heard before.
If KIRO or KOMO are considering putting their AM programming on FM, I would recommend moving the FM transmitter to Capital Hill (if possible). You want that programming in the buildings in downtown Seattle and Bellevue. The Cougar/Tiger mountain stations all have a tough time in the I-5 canyon through downtown Seattle. If Bonneville really does get 104.5, it should try for Cap Hill.
That said, the terrain of Seattle argues against going to FM. KOMO and KIRO are two of the best 50k's on the coast, and their signals reach into every ravine and canyon from Lacy to Marysville. And engineers at both actually care about AM fidelity (see also: Channel, Clear).
But the spoken word stations that survive into the next decade will be on FM. Too many people 40 and younger have no idea there is such a thing as AM radio (except sports radio fans).
RJ