BigA: By the first three of those standards, this one should have been a no-brainer. Each of the three cable channels has at least one anchor and a control room hot 24/7 for breaking news (though CNN now farms that duty out to CNN International after midnight ET). Each of the three has satellite transponder space available (and already paid for) for uplinking breaking news, 24/7. CNN could have cherrypicked from any of the big three Seattle stations' ongoing live coverage and MSNBC could have picked up KING-TV. It appears Seattle's Fox affiliate, KCPQ, was late to the live coverage last night, which might have impeded FNC's ability to pick up its coverage had it chosen to do so.
That fourth standard, "impact," is a little fuzzier. In the light of the next day, the story doesn't seem to have too much big national impact - nobody died and the cause appears to have been a wayward truck rather than a massive structural failure. But when the headlines hit last night, I think a good national news editor should have erred on the side of too much, rather than too little, coverage. I-5 is a massive border-to-border route, after all, and Vancouver to Seattle is a fairly heavily-trafficked corridor in particular.
FredLeonard: What's "curious" about the CBC covering it heavily? Vancouver is one of the largest cities in Canada, and I-5 is the major connecting highway that carries commerce southward from Vancouver to the entire U.S. west coast. The disruption of I-5 traffic is a major issue for Vancouver, and thus for much of western Canada.