I guess I'd like to interject here for a minute about the battle of Hoth.
The Empire Strikes Back is my thing, so I would like to contribute a little bit to this conversation.
The thing about the battle of Hoth that you have to keep in mind is that the Rebel Alliance never intended Hoth to be a permanent situation.
The entire base, and how it was staffed was purposely designed to be evacuated, and abandoned on a moments notice.
The very instant that the rebels thought something was up (when Han and Chewie encounter the probe droid), they began the evacuation...this plan of action was put into motion before the Imperial fleet even arrived in the system.
The shield was in place simply to buy them some time in order to facilitate the evacuation. Without that shield, the entire outpost could have been obliterated from orbit in a few moments. That shield forced the Empire to commit resources to a ground assault, and that process gave the rebels precious moments to keep working on getting people off world.
The suggestion was made about using Y-Wings, and X-Wings to attack the Imperial Walkers...where I'm sure this would have been very effective against the Imperial armor, it simply was not practical since the X-Wings were needed to provide escort for the escaping transports...
Take a look at this pic:
http://dawnofthejedi.files.wordpress.com/2010/06/echobase.jpgThis cutaway shows a great rendition of how part of Echo Base was set up...
The fighter/bomber compliment at Echo base was probably quite small, even though the Wookieepedia states 60 fighters, and 30 medium transports...in that pic alone I count 20 X-Wings/Y-Wings, and 4 medium transports. There would have to be 2 more levels of structure to accommodate a fighter compliment of that size...not to mention the space you'd need to store another 26 medium transports...I just don't find those numbers very sensible.
When you consider that the bulk of the Rebel fleet was out in space somewhere hiding as well...I would wager that the majority of the fighters, and attack craft were left with the fleet to protect the capital ships, run patrols, and whatnot.
Not to mention...how long did that battle last? Was the Imperial Navy so incompetent that it allowed 30 transports to slip through? Going back to the Wookieepedia, it states that 17 of the transports were destroyed...it also talks about Renegade squadron getting into combat with Darth Vader...and here is where I start to lose focus...Reading the entire Wookieepedia entry for this battle makes it seem more like a campaign lasting a couple of days versus a quick, decisive battle and retreat by the rebels. I love EU as much as the nerd standing next to me, but simply going off the original information given to us by the film, the outcome of the battle of Hoth was determined by the Rebels before the base was even constructed.
Which leads me to an even bigger question...why was Echo base needed at all? We know there are smaller rebel outposts scattered across the galaxy, but the bulk of the infrastructure lies within the main fleet itself...this is demonstrated at the end of Empire, and most of Return of the Jedi.
I love talking about stuff like this.