Here is Chabad's explanation of why the Torah readings differ between Israel and the diaspora:
http://www.chabad.org/library/article_cdo/aid/927435/jewish/Different-Torah-Readings-in-Israel.htmQuestion:I enjoy your website and regularly visit the section on the weekly Torah portion. Recently I discovered, to my great surprise, that on the top right-hand side of the Parshah homepage, you write: "In Israel, this week we read: .... [here appears the name, and a link to, the following week's Torah reading]."
What is going on?Answer:Once in several years, for a few weeks, different Torah portions are read in Israel and in the Diaspora. This year (2009-5769) happens to be one of those years.
Why does this happen? Here is the basic idea:
1) The Torah is apportioned into 53 readings, and each Shabbat we read a portion according to a predetermined order. When a holiday falls on Shabbat, we substitute the reading of the weekly portion with a section from the Torah that relates to that holiday.
2) In Israel we celebrate most holidays for one day, and outside of Israel for two days (the second day is called "The holiday of the Diaspora").
This year, the holiday of Shavuot started on Friday. In Israel it was celebrated for one day. The next day was Shabbat and everyone read the Torah portion of Naso.
Outside of Israel, however, the holiday was celebrated for two days. On Shabbat, everyone read the Torah portion for the second day of Shavuot. The Torah portion of Naso wasn't read until the following week—by which time synagogues in Israel were already up to the next portion, Beha'alotecha. That's how Diaspora Jews ended up behind by one portion.
But no worries: We in the Diaspora will soon catch up with our Israeli brethren. How? Because on the Shabbat of the 12th of Tammuz (July 4th), those in Israel will read the Torah portion of Balak, while we will read two portions—Chukat and Balak—joined together. Once again, all the Jewish People will be in synch.
Rabbi Mendy Kaminker,
Editor, He.Chabad.org