An epiclesis is a petition, and its position inside the eucharistic prayer decides a great deal that its wording does not. In the Byzantine anaphoras the priest recites the account of the institution, continues with the remembrance, and then asks God to send the Holy Spirit upon the assembly and upon the gifts set out, that the bread may become the body of Christ and what is in the cup his blood. The deacon and the priest bow, and in Slavic practice the troparion of the third hour is inserted at that point. Because the petition comes after the narrative, it reads naturally as the request that the narrative has led up to, and the Orthodox understanding follows the shape: the church asks, and God answers.
The Roman Canon has no petition of that name. Two prayers do comparable work and they stand on either side of the narrative, the first asking God to bless and approve the offering and the second asking that it be borne by an angel to the altar on high. Latin theology, reading the narrative as the form of the sacrament, had no need of a request for the Spirit and did not develop one. The eucharistic prayers added in 1969 restored an explicit invocation, and put it before the narrative rather than after, so that the Roman rite now has an epiclesis in a position that keeps its own account of consecration intact.
The same word covers the invocation of the Spirit at baptism, at the blessing of chrism and at ordination, which is why liturgical writers treat the eucharistic epiclesis as one case of a general pattern in Christian prayer rather than as a device peculiar to the eucharist.