This just occurred to me.
The first Death Star has only one weak spot, an exhaust port. The second would've had no weaknesses, had it been completed, and even incomplete could only be destroyed by blowing up the central reactor.
Think about this logically for a second.
The Death Star superlaser blows up one planet, which likely has shields, and is prepared to blow up a second one, which is almost certainly shielded.
Small explosions on the surface of the Death Star cause explosions inside.
The Executor crashing into the second Death Star is described as severely damaging the station.
So we see that normal attacks and explosions most certainly do affect the Death Stars. And we know that continued attacks from ships as small as TIEs can bring down a Rebel Cruiser. Plus, the Death Star carries a weapon that can easily disintegrate a target many times its own size, regardless of shielding.
So, in essence, Lucas expects us to believe, despite all the onscreen evidence to the contrary, that the Death Stars somehow escape all logic simply because they're big?
We're supposed to buy into the fact that this thing would survive hours, even days, of continued bombardment by the entire Rebel fleet without any ill effects?
Hell, why don't the Rebels build their own superlaser? Wouldn't a superlaser take out a Death Star, no problem?
And if an ion cannon could take out a Star Destroyer so easily, and they're pretty standard weaponry, why couldn't a large ion blast simply disable the entire Death Star and take it out of commission?