Yes; it is true that there are two, and maybe more under those dialects, armenian dialects. Western armenian is based on the kind spoken in Istanbul (we call those armenians Bolsahye, Bolis is armenian for Constantinople/Istanbul, probably from greek "Polis" for city) and is spoken in the diaspora, whereas eastern armenian is based on the kind spoken in armenia, and is spoken there, and in Russia and Iran.
And even then, under western, you could say there is a lebanon accent, an istanbul accent (my grandfather has a really thick one, it is different than regular western for sure...), an Iraq accent, syrian, etc etc. It's almost impossible to say, but the one most taught is standard western, which is from istanbul.
The only division, I think, in eastern, is between Iranian Armenians and the others. Russian armenians all basically come from armenia itself within the past 100-200 years, maybe most in the past 100 years, since Stalin and Beria (Beria especially) being Georgians, thought they could justify annexing armenia into georgia if they deported enough armenians out (to under 700,000).
If someone speaking western spoke to someone who only knew eastern, they might confuse each other at first, but in a short time could probably understand each other. I'll let you know when I get back from there in late July (I am going to help teach kids english and fix up some houses, and of course see the sights...)
Armenians in Armenia and Russia (those speaking eastern) also use a "soviet" alphabet with some different letters. Armenians in Iran and the diaspora use the original alphabet.
My family comes from Evereg-Fenesse (http://en.wikipedia.org/wiki/Develi and my cousin's website: http://evereg-fenesse.org/_wsn/page2.html) which borders the turkish town of Develi. The other part of my family comes from a place near Sivas...one village called Ishan and the other Horuhoun (I can't spell it)...one of those was renamed Dozuglu or somesuch.