This is a consequence of the relatively recent occurence of satellite TV channels broadcasting US shows within a week or two of them being aired in the US.
In the good old days British TV companies would tend to buy a complete series from the US, perhaps months or years after being shown there, and so could schedule a complete week-by-week run of the entire series. Now we are seeing more cases of the series being "bought" before the episodes have even been filmed.
The US TV audience is traditionally more accustomed to having mid-season breaks and interruptions due to major sporting events and this can be illustrated using US broadcasts of NCIS Season 7 -
Eps 1 - 5
1 week break
Eps 6 - 9
2 week break
Ep 10
2 week break
Eps 11-12
1 week break
Eps 13-15
2 week break
Eps 16-18
2 week break
Episode 19 is not due to be aired in the US until 6th April so do not expect it on FX before 16th April.