I can't help but feel the need to "kick my can" into the pit, as it were. Never mind my crappy attempt at a folksy saying. Jamie is indeed correct, in that the matter "levels" of canon. I can't remember the levels off the top of my head, but it is largely considered that there is a certain matter of "common sense" that must be applied to the games. Many of us are guilty of attempting to use the games to our advantage, but when it comes down to it, no matter who it is is in bad form as an RPer in doing so. It is also bad form to discount a resource, because it is, as you say Crin, "a picture book essentially". That would also, in essence, discount just about every guide every written for Star Wars... ever. I can't think of a single dedicated source book that doesn't have illustration to it, and in the case of Incredible Cross-Sections, the illustration is meant to be in-depth and explain the technological and mechanical aspect of Star Wars. They are also very helpful in understanding and interpreting Star Wars physics, which are indeed unique in many aspects to real world accepted Newtonian physics (i.e. there being a top speed for ships in Star Wars, when in the real world an objects speed relies simply upon the amount of thrust that an engine can give and the amount of fuel it has, along with gravity, etc. A gross simplification, bu there ya go; an example). While I would say you are right on the Taris example, to a degree Crin; Jamie is also right in the advancement of technology. I mean, fast forward about thirty years from where we are now in the canon and the technology from the Clone Wars doesn't hold a candle to modern technology of that era. If you do want to use games as such a definite source, then pop in Empire at War: Forces of Corruption and see how badly you can rape an Venator Star Destroyer with an Imperial Star Destroyer. Should we take this as absolute fact? No. Should it impact the perspective of such an event in the RP? Yes.
On the case of your Taris example, were we to take it literally; yes, I will give you that it takes a lot of time for the section of Taris in the shot to be damaged, let along destroyed. The problem in this example is the fact that in the case of Taris, you are talking about a eucenompolis, or city planet. So, the words planet and city are equivalent, and the building are, on average, throughout the planet, several hundred stories high. Regardless of firepower, that is big amount of material to blast through, and blast through it the Sith did, across an entire planet's worth of it. Now, replace Taris with Coruscant. Coruscant is larger, and astronomically better defended, but let's keep defenses out of this. Take the same barrage to Coruscant, and yes, it isn't going to make a dent. Now, replace said planet-wide city, with a smaller one. Chicago, Illinois. Notice the gaping hols ripped through those buildings in the video? One of those could topple the Sears Tower, maybe two if placed poorly. If I must also use another real-world example, and a grim one at that (and debatable to some), but on September 11th, 2001, two towers, considered the pinnacle of skyscraper design at a time, were brought down by the mere impact from a single 767 aircraft each, and the resulting heat damage from the burning of said aircraft's fuel. Those aircraft are nothing compared to the energy within a turbolaser blast. That is another perception I think you seem to have Crin, and I apologize if I am incorrect, but kiloton and megaton are not done just for nuclear and atomic weapons, but, and while improper, can be done for turbolasers.
So, say, and I can't remember the ICS numbers, that a turbolaser is rated to give off a blast worth... 10 megatons. One thing to keep in mind, this is not material energy, but, well, just energy. Now, when it says that, imagine the blast of a 10 megaton nuclear bomb, minus the radiation factor, and focus it into a precise point. And there you have it, the damage from a turbolaser. Keep in mind too, we have set off many nukes on our planet, without many problems. There are at least 2,000 nuclear bombs, ranging from the low kiloton to the maximum thus far of 50 megatons, that have been detonated within the past sixty-five years, with up to 140 per year. Okay, I'm going off-track here, and how damaging a nuclear war would really be compared to our fears is irrelevant. The point is, there is little to no radiation involved, at the lower level at least. Okay, big point is, and an undeniable one, is for a regular city, a turbolaser blast is pretty devastating, but not so much for a city-planet.