I looked at one of the usually most balanced Israeli newspapers and their headline was that that the US/Israel ties are fine. This is interesting because it is obviously addressing an underlying concern - that Netanyahu's actions do not harm that relationship.
There explanation shows that this situation was NOT really related to any hurt feelings on the part of Netanyahu.
Netanyahu was due to arrive in Washington on Monday evening and was set to take part in three or four conference sessions the follwoing day, before returning to Israel on Wednesday.
Officials said the PM canceled the trip over fears that a group of Muslim states, led by Egypt and Turkey, would demand that Israel sign up to the international Nuclear Non-Proliferation Treaty, or NPT.
A senior government official told Haaretz that that Israel was "disappointed" with developments in the run-up to the conference.
"The nuclear security summit is supposed to be about dealing with the danger of nuclear terror," the official said. "Israel is a part of that effort and has responded positively to President Obama's invitation to the conference."
The official added: "But that said, in the last few days we have received reports about the intention of several participant states to depart from the issue of combatting terrorism and instead misuse the event to goad Israel over the NPT."
http://haaretz.com/hasen/spages/1161776.htmlNow, the official's comment is telling - this is a NPT conference! It is also interesting that that effort is supposedly led by Eqypt and Turkey, which are with Jordan the countries Israel is on best terms with in the Arab world.
(The Jersualem Post pretty much says the same thing.
http://www.jpost.com/International/Article.aspx?id=172707This agrees with your second link, which said:
"The summit, which will include 47 nations, is part of Mr Obama's agenda towards nuclear disarmament and non-proliferation. Israel was initially due to send a low-level delegation but Mr Netanyahu agreed to take part after he received reassurances from American officials that Israel would not be forced to disclose its nuclear capabilities or commit to reducing them. Israel has long maintained a policy of 'nuclear ambiguity', in which it neither confirms nor denies whether it has nuclear weapons."
Here, the interesting thing is that the US could really not guarantee that other countries - at a NPT meeting - would not bring up Israeli nukes.