What was the point in reaching the Vault in Borderlands?

It is true that the Borderlands ending is one of the most disappointing endings that a game ever had. Quoting Paul Helquist, senior designer:

I think what's great about where we did leave the player is that we have pretty much infinite options of where we want to go next[...]
[...]The ending of the game, for better or worse, didn't paint us into any corners.

So what I presume is that they will dig deeper into the story around the Vault in Borderlands 2 (released somewhere between 04-2012 and 03-2013).

To give you a little bit satisfaction from the ending, consider this explanation I found on the web a while ago, that made the ending slightly more acceptable:

The world is named Pandora, implying that something can be opening from it, this being the Vault. The legend of pandora's box detailed that the greatest evils of mankind were locked away in it, and someone was foolish enough to open it. Once the evil was released only one slither of goodness was left within, and that was hope. So think of the Destroyer as evil in a physical form, sealed away in Pandora's box so to speak, and the character you are playing is the one final hope for the planet.

I do hope that the ending in Borderlands 2 will be a better one than its prequel's.

I the context of Borderlands 1 I guess the point was just a challenging boss-fight to finish.

However, in Borderlands 2 they flesh out the story (includes mid-game spoilers):

Angel and the Hyperion corporation were manipulating the player all along. They wanted the player to open the vault as it would facilitate the mining of Eridium on Pandora.

It's also revealed (even later game):

The 200 year limit was due to the time it takes for the key to recharge on it's own. With a Siren (suitably charged by Eridium) the key can be recharged in a few years.

Finally, in the end game for BL2:

So all through Borderlands the player is being manipulated so that Handsome Jack and Hyperion can get the key. Jack already has a Siren who can recharge the key, and has another 'vault' that he wants to activate using it.

Well in the Borderlands official guide book it is said that the Eridians sacrificed their whole civilization to imprison the destroyer in the vault and to create the Guardians who protected the vault from being opened.

Also 4n631 or Angel says that she didn't tell the main character what was in the vault just so that she could get him there. She expresses regret over the deception but says that it was the only way to get the vault hunter there.

She says in the dialogue at the beginning of the battle that the destroyer is immortal in it's own realm but that when it enters this world it will require a host which is vulnerable. So actually the whole point of the game was to kill the Destroyer so that it couldn't wreak havoc in the universe at least for the next 200 years :)

I didn't like the ending either at first but when I read this it gave me some sort of weird satisfaction like: "Oh, so there WAS a meaning for all this stuff after all" Although I do hope that Gearbox will do a better job with Borderlands 2, maybe let us hunt for riches FOR REAL this time?