There is a bug here, and "network congestion" is in fact not a bad way to put it without going through the whole technical explanation. Remember that MtGox don't use bitcoind to process bitcoin transactions other than for block validation. It just doesn't scale to the amount of addresses they have (primarily) and transactions they have to keep track of.
Sometimes transactions take a very long time to confirm. E.g. due to sending a small transaction without fees (user error), or (the BUG) trying to use a coinbase transaction with less than 100 confirmations. Sometimes transactions fail to confirm for reasons I can't explain either. You can get all og MtGox's unconfirmed transactions which are at least 2 hours old from the URL below, and use it to verify my claims. It is updated every 20 minutes: https://data.mtgox.com/api/0/bitcoin_tx.php
When a transaction isn't confirmed after ~24 hours, MtGox tries to solve it by issuing a high fee transaction to itself where it spends one or more of the inputs of the unconfirmed transaction. This will invalidate the unconfirmed transaction. When the invalidating transaction has 6 confirmations, MtGox will issue a new transaction for the withdrawal, and this usually confirms at once. But due to the coinbase bug, this may also be a troublesome transaction. (The reason why support will ask you to wait 24 hours.)
Usually the list of unconfirmed transactions is short (~100 micropayment transactions with no fees). This is rebroadcasted in longish intervals, but a rebroadcast doesn't help much because miners don't even forward those transactions with no fees. Much less mine them. When the list get very long, this becomes a bottleneck ("network congestion"). And it does for several reasons. The main reason is the coinbase bug (known for a long time, and they should rally get this fixed), which leads to cancellation transactions, and when the cancellation transaction doesn't confirm, there will be another, etc.
So this is just a bug, not a form of capital controls. AFAIK everyone have received their BTC withdrawal eventually. But I am sure you conspiracy theorists won't let facts affect you.
On the other hand it is Sunday today. Sunday is MagicalTux's coding day. Let's hope fixing this bug is on top of his TODO list.