If you were to have followed the news you'd have known better than saying that...
And no, the government has indeed not blocked the purchase of Airbuses by UA, NW or US, simply because these are all private companies, and the government can not interfere with their fleet choice. However, El Al is state owned, and Israel recieves billions in aid from the US government, so the US government can put pressure on the Israeli government, as they did in this case. El Al had even signed an MoU with Airbus for 5 A319s plus 5 options. Same happened again with the planned purchase of A330-200s recently.
But, back on subject, the size is probably indeed the main reason for them not being happy with it.