User blog comment:Braveangel/About planetary defenses/@comment-737801-20100423194505

In BSG also the ships had computer networks that the Cylons hacked into to disable all ships except for the Galactica and the Pegasus, as far as the series explained.

Dreadnoughts are at the Citadel to provide additional defenses and reinforcements are never very far away. Defenses at other places couldn't be feasible because as every series of scifi that I have seen has played this card and you can only hold them off for so long before they land. What I man is that defenses are more of a nuisance than a full weapons grid. As for major planets, they probably have several layers of defense, fleet, orbital positions, and then ground defenses. Fleets are the backbone of any space faring people and would logically be the main portion of defense.

Also you have to consider that the Citadel was discovered and not constructed by the races of Mass Effect. I'm sure that stations built by the races have more guns and defenses because they could build them into the construction. The Citadel was constructed who knows how many millions of years ago, than the probably the Reapers stripped its defenses to the bare minimum because otherwise they might be turned against them.

Again though back to the Dreadnoughts, they have to be affective at far and close ranges. They have a lot of broadside guns that can be used at those ranges. Their main and most powerful gun can only be used at long ranges because it is designed to be used that way. If you were to create a ship that is only affective at long range, especially one the side of a dreadnought, then you just wasted billions of credits.

So my opinion why dreadnoughts are at the Citadel, they represent power, they help moral, and if enemies get close, they get alongside, and fire in full broadsides. If you have seen footage from Star Wars Episode III, the opening battle of Coruscant, where Grievous’ ship is engaging the Republic Cruiser before taking a nose dive, then you know what I mean.

Man I love that battle, however Endor was better. Personal opinion.