The Gemara discusses saying kerias Shema when one is torud with another mitzva such as his first married night or even if he is agitated over some unfortunate event. A distinction is made between a choson and one who suffers a loss. A choson would not say kerias shema on his first night. If one's ship sinks in the sea, he would still have to say kerias shema. Didn't we learn elsewhere that when a person returns from a long trip he is potur from davening for a while? The reason presumably is that he's too fartumult and his mind is not at ease enough to concentrate even minimally on his tefilla. Why is that different from our case? Is there a distinction being made between kerias shema and tefilla?
In addition - is there a philosophical, linguistic or hashkafic difference between Ahava Rabba and Ahavat Olom?
The Halachah exempting someone who returns from a journey (or anyone whose mind is not clear for that matter) is a Gemara in Eruvin 65a, and as you suggest, refers specifically to Tefilah (which a. is only mi'de'Rabbanan, and b. requires more Kavanah). You did well to make the distinction between the Sh'ma and Tefilah. Actually, our Gemara in B'rachos makes the same distinction on 16a. with regard to workers, who may recite the Sh'ma on a tree, but who may not say the Amidah there because, as Rashi says, Tefilah is 'Rachamim', and requires Kavanah, which basically conforms with the Gemara in Eruvin.