There is no "to [your] advantage" unless the price was wrong when you clicked on it, in which case that is a problem with their price feeds. If you try to buy or sell at the CS quote, and the CS quote correctly reflects the underlying market, it is not to your advantage if a dealer fills the order 30 seconds later when the market has moved in your favour - it is simply what you would expect after clicking on a price.
As for it not occurring too often - I may have agreed with you at one point. When my trades went to the system dealer, I would get "price no longer valid" perhaps once per week in a genuinely fast market. On dealer intervention, if the market moved more than the spread in my favour I would get rejected without fail. Without fail.
No requotes is nice - a deal is either done or it isn't. However, I don't know if that is something to be saluted for. Consider that with CMC, if a trade is declined and you get a "requote", all that happens is that a box jumps up showing their best bid or offer (depending on whether you tried to buy or sell), and a chance to either deal on the price or not. If you do not deal, nothing gets done. With CS, you have to close the "price no longer valid" box, enter your stake in the appropriate market, press trade, wait for the box to come up, and then trade again. This takes considerably longer than it would if you had the option to trade on a "requote". Of course, this isn't much of a problem, but a requote is a lot faster than pulling up a new ticket and therefore favours the client in exiting a position in a fast market.
Remember, when CS reject the price the effect is the same as a requote. They have rejected your offer, you have nothing done, and you have the option to deal on a new price or not at all. "no requotes" just means you have more clicks.