עבר הירדן

(the following is based on research done by a dear friend and mentor, who complied this from various achronim including: משנת רב אהרון, ר' דוד קרלינר, ר' מנחם זמבה, הגרי"ד סאלווצייק, משך חכמה and others)
the ran comments that one may not bring the Omer from עבר הירדן. (there is a rashi somewhere in Sanhedrin that argues) What you see from the Ran is that the Kedusha of עבר הירדן is different then that of the rest of Eretz Yiroel. The achronim explain that the land of עבר הירדן wasn't promised to our for-fathers, rather was captured by Moshe as כיבוש רבים, this gives it Kedusha of Eretz Yisroel but on a lower level.
You might ask, if עבר הירדן has a status of כיבוש רבים then why doesn't have the same issues of סוריא that, according to some rishonim, is problematic because it was captured by Dovid before the rest of Eretz Yisroel was completely conquered? answer: that here Moshe had no choice in conquering Sichon and Og, because they wouldn't let them pass, therefor it is better then סוריא
Interestingly, the achronim say that there is another נפקא מינא - like this: The "mainland" of Eretz Yisroel doesn't require כיבוש to give it its Kedusha, this is why for חלה all that is needed is that you fulfill the תנאי of "most people coming into Eretz Yisroel", but you don't need כיבוש, and once the Jews came in the land they were obliged in the Mitzvah of Challah. Other mitzvos, however, need also כיבוש for them to take effect. so we have in mainland Eretz Yisroel itself 2 levels of Kedusha, one that is G-d given and one that requires our כיבוש
interesting to note that in the Mishna in Kelim where it lists the 10 קדושות of Eretz Yisroel, עבר הירדן is not listed, because that mishna deals only with the other type of Kedusha, that of "mainland" Eretz Yisroel with its source - the בית המקדש.
Lastly, on a מחשבה note you see that Eretz Yisroel is a place where the Kedusha (at least parts of it) is predicated on 2 factors, G-d's promise thru prophecy and OUR input in כיבוש. The idea being that the land is the place where we join G-d in "finishing off the work needed to be done" (reference Rebi Akiva on Milah). if we are to G-d as a bride is to a groom, the land is our house where we practice our covenant of marriage.
I have my own thoughts why, based on the above, the Omer cannot be brought from עבר הירדן, but we'll leave that for now...