That's not necessarily the case. They sold the majority of their coins months ago. Many of us have held a large amount of coins and have been staking them since the summer. I have been buying coins on a weekly basis since October.
That chart shows the percentage of coins (PoS and PoW) paid out over the last 100 blocks. Many of the wallets on the rich list belong to exchanges.
No they are still holding a lot of their coins.

It makes no sense for them to keep them that way especially for a pump and dump as everybody will know they moved and to where and likely dump as soon as that happens.
Those are probably exchange cold wallets. If you take a look at the largest wallet feature you will see there is no cryptsy or poloniex so that could be either of them or both.