I'm curious why studio monitor speakers are recommended much more for PC opposed to good hifi bookshelves? I get that it's easier to get active monitors, but decent t-amps are pretty cheap too.
Passive speakers need some room for an amp somewhere. High-order crossovers and EQing also eat up some efficiency, not to mention the cost for still rather non-ideal capacitors and inductors. (A 4th-order crossover is pretty easy to do in an active speaker, in a passive one it'll get expensive. High-order crossovers are good for getting crossover frequency down - which in turn allows for wider dispersion while keeping good integration of woofer and tweeter - with reduced risk of the tweeter burning up. The overlap in frequency response also gets smaller, and thus the associated anomalies in vertical dispersion.) It's also much easier to integrate frequency response tweaks.
Maybe the most significant argument: Monitors are built for work. You don't pay for fancy looks, and margins aren't as high as in the hi-fi market in general (at least in the "mainstream" range). You're also more likely to find ones built with state-of-the-art construction principles somewhat further up the ladder.
Both active and passive speakers can be optimized for varying listening distances, but classic hi-fi speakers with widely spaced drivers and low-order crossovers tend to be rather uninspiring in nearfield use.
Anyway, there are good and bad designs in both camps. (There's a good bit of contracting work going on in this area anyway.) It's just harder to weed out the hi-fi speakers because there's such an awful lot of them.
