Mining pools, exchanges and processors have no direct say. All that is needed for the BIP to be merged is agreement among the lead developers. That would be Van der Laan, Gavin Andresen, Jeff Garzik, Gregory Maxwell and Pieter Wuille. Correct me if I missed a name or am in error.
Miners have most of the power.
No.
We do. (assuming you hold any bitcoins)
The power dynamics is a stratification of users/nodes/developers/miners/merchants and exchanges; each exists with differing capabilities to exert influence on each other.
Many Miners have the most power as they are in at least 3 of those categories and sometimes 4. A user that doesn't host a full node is only in one of those categories therefore is more limited in their vote/abilities.
Meritocracy is really an critical aspect within bitcoin. It isn't just Proof or work with regards to hashing but proving ones work with developed and tested code, proving ones work with a hosted node, proving ones working with the most hashing power, proving ones work by client base or political power, ect...
If you only own bitcoin than your vote is counted far less than if you actively contribute to the ecosystem.