Tehilim 146:5 says אַשְׁרֵי--שֶׁאֵל יַעֲקֹב בְּעֶזְרוֹ: why Kel Yaakov? Why not Kel Avraham or Kel Yitzchok?
Reb Shmuel Houminer in Eved HaMelech answers this question, explaining that Yaakov is the one patriarch who truly verbalized that everything comes from Hashem. Therefore the verse is saying that the one who is truly blessed is the one who recognizes that everything comes from Hashem.
"Yaakov vowed, saying, 'If Hashem will be with me and guard me on the way which I go, and will give me bread to eat and clothes to wear...'"(Bereshit 28:20) Yaakov was saying, "I always feel that Hakadosh Baruch Hu, watches over me, and provides me with bread to eat and clothes to wear." "May I return in peace to my father's house"(Bereshit) Rashi comments "In peace -- without sin, not learning from the cunning of Lavan, not being led astray by anybody or anything in this world. "Then Hashem will be my G-d" (Ibid) Then it will be ingrained in my heart that Hashem is G-d, there is no other than Him, no external power other than His. Everything is full of His oneness. Based on this, Yaakov immediately commented, "He does justice for the oppressed, He gives bread to the hungry"(Tehillim 146:7)
I was at a Bar Mitzva this week and the speaker said a beautiful reason why it says Kel Yaakov. When Yaakov left to go to Charan, Elifaz chased after him and in the end took all his money. Yaakov arrived in Charan destitute and penniless. When we are Davening we are saying Ashrei SheKeil Yaakov B'ezro - just like Hashem helped Yaakov when he was totally down so should Hashem help us when we are totally down.