First, let us assume that Durasteel is about twice as strong as depleted uranium.
Thus, Turbolasers probably don't do that much damage. It's notable that ships in Starwars can survive hits from turbolasers unsheilded. If you go by the 'official' *COUGHfanboyCOUGH* calculations, the yield comes out significantly larger than an A-bomb.
A direct hit from an A-bomb, all things considered, should utterly vaporize ANYTHING made of depleted uranium. Even if Durasteel was three times as strong as depleted uranium, it would still vaporize when hit by a nuke. Thus, a ship without shields in Star Wars would be vaporized by one or two hits.
Another inconsistancy: How come the Hoth base (Echo base) wasn't vaporized by the orbital bombardment when its shields went down?EDIT: And after the empire knew that their targets had escaped. Speaking of which, if the Empire was smart they would have annihilated Echo base as soon as they could.
Now, a few other things to keep in mind:
-Star wars ships, especially Imperial ones, have VERY vulnerable shield generators. The ISD's shield generators are (stupidly) unsheilded themselves. Whoever designed this ought to be spaced.
-Starwars 'lasers' fire bolts of "coherent light". Fairly absurd, eh?
-Wookipedia lists no exact power level for turbolasers, because there are MANY estimates as to how powerful they are. (see for yourself: http://starwars.wikia.com/wiki/Turbolaser
-George Lucas seems to consider anything cannon, no pun intended.
(And if you think Star Wars has things far too large to be built, I'm writing a book with a ship called the Darkspire that has its own class: a solar Dreadnought. The ship is about one Astronomical Unit long; that is, 150 million KM
. Beat that!)