I think the cops probably need to do more old-school investigating and undercover work.
This is part of "old-school investigating". The dog is to help them execute search warrants. The child porn can be stored on any kind of electronic storage medium, and that can be hidden pretty much anywhere in the house. It's a ton of failure-prone work to dig all that stuff up so you can search it.
In this particular case, it actually involves undercover work, too. Investigators get on P2P file sharing networks or infiltrate underground trading rings (which is sometimes pretty tough) and find people trading illicit material. Often, judges want a fair bit of supporting evidence that they're intentionally sharing explicit material (since everyone knows the "a virus did it" defense), so they'll get the target to reveal information sufficient for a warrant. (On top of that, they have to make sure the person is within their jurisdiction.)
Often times, a child porn case starts because someone calls the cops, and that requires a fair bit of proper investigation, too. Usually the accused is in contact with a child, and you have to figure out if something is going on there. Sometimes it's people planting evidence to get back at an ex-boyfriend or something, and you want to eliminate that possibility, too. (One guy tried to steal his neighbor's wife by planting CP on his neighbor's computer. Really not a great plan.)