Frank - there are a couple of reasons for this.
First being FXDD's meta trader platform is obviously a deal desk model. Pricing from that model probably comes from one bank, maybe more but who knows. Most dealing desk models have relationships with multiple banks. However, they will probably only use one of those banks prices to offer to their clients. They will take those prices and mark them up. The only reason they would use one of their other providers is because provider one's feed went down. Most use one bank as their main source of liquidity becuase if you throw more volume to one bank you will get better clearing fees and prices from that one bank. If they spread to multiple banks their clearing fees will end up being higher even though this might benefit the trader. They have multiple banking relationships for back up in case one goes down and so they can offset their risk with the bank showing the best price.
With that being said, a dealing desk might have a better spread because their main bank is showing a better spread then a lot of the others. This happens a lot depending on the banks inventory and risk parameters. The other reason the dealing desk might be showing something better is because they are making a market that they are comfortable with and they feel they can still profit from the prices they are showing. Banks do many things during news; everything from graying out prices to widening.
The most important thing to remember is size. If you are doing a standard lot around news you probably wont have a lot of trouble getting in if your broker is offering a reasonable price. However, try dealing on that price when you are trading 10 standards or more. I guarantee you, you will have a lot of trouble. The more size you trade, the more risk you are giving your broker. So if you add your million dollar trade to all the other small traders trying to trade that number you will see that the broker has to offset a lot of risk with their banks who might now want it. So the banks will turn around and widen the spread on the broker because of all the risk. That will then be shown to you from your broker.
ECN's generally should show better but it all depends on how many liquidity providers they use. If you see worse with an ECN then a dealing desk on a constant basis you should make the assumption that the ECN's liquidity is not as deep as the dealing desk broker.
First being FXDD's meta trader platform is obviously a deal desk model. Pricing from that model probably comes from one bank, maybe more but who knows. Most dealing desk models have relationships with multiple banks. However, they will probably only use one of those banks prices to offer to their clients. They will take those prices and mark them up. The only reason they would use one of their other providers is because provider one's feed went down. Most use one bank as their main source of liquidity becuase if you throw more volume to one bank you will get better clearing fees and prices from that one bank. If they spread to multiple banks their clearing fees will end up being higher even though this might benefit the trader. They have multiple banking relationships for back up in case one goes down and so they can offset their risk with the bank showing the best price.
With that being said, a dealing desk might have a better spread because their main bank is showing a better spread then a lot of the others. This happens a lot depending on the banks inventory and risk parameters. The other reason the dealing desk might be showing something better is because they are making a market that they are comfortable with and they feel they can still profit from the prices they are showing. Banks do many things during news; everything from graying out prices to widening.
The most important thing to remember is size. If you are doing a standard lot around news you probably wont have a lot of trouble getting in if your broker is offering a reasonable price. However, try dealing on that price when you are trading 10 standards or more. I guarantee you, you will have a lot of trouble. The more size you trade, the more risk you are giving your broker. So if you add your million dollar trade to all the other small traders trying to trade that number you will see that the broker has to offset a lot of risk with their banks who might now want it. So the banks will turn around and widen the spread on the broker because of all the risk. That will then be shown to you from your broker.
ECN's generally should show better but it all depends on how many liquidity providers they use. If you see worse with an ECN then a dealing desk on a constant basis you should make the assumption that the ECN's liquidity is not as deep as the dealing desk broker.
Sorry to spoil your joy but I've got to say this.
ALL OF IT at one single second 
