While that certainly can be the case, I would assume on basic principle that more people stay in Silver that are Silver-level than leave it. Effort is still effort, and the amount of effort to overcome the skill disparity is not small as the average player skill increases.
This is part of the unavoidable truth that Churn forces a game into.
If a game generates new content, new and old players will explore the game.
If a game stops generating new content, new and old players will stop having things to explore.
So, years of additions are certainly a mountain to climb for a new player, but there's no requirement to learn everything at once. You can play one class of ship for years and still be learning, and that's before even going down the next Path to Mastery the game offers.
In the end, it's a complex problem and it's a grueling industry. We have a great game, though... and it continues to grow which is a beautiful thing.