Huge reading comprehension failure for several people from this source quote until this post.
Nowhere in that reply did they mention costs for upkeep and upgrades being locked in. Stephens post is about the initial 5,000,000,000 figure, nothing else.
They do not want everyone to get one in the beta so people are testing the mechanics from owner and visitor point of views. That is the data that is being gathered so the upgrade and weekly costs can be adjusted from there.
The Beta lasted less than a week so the upkeep and maintenance costs were pretty immaterial for the beta and since it only lasted a week they gathered no data on maintenance and upkeep costs. They kept all the costs to the same they expected them to be in the live game probably because they wanted to see how they were accepted. Most people are quite happy with the purchase price, that doesn't seem to be the issue, big ship, big price, but the short beta gave them no data on the maintenance and upkeep except for the feedback they are experiencing through the forums.