Often times I'll hear an enterprise architect discuss their concern over how much support they get from their company's CIO or CTO. "If they'd only back me more often, I'm sure we could more things done." Comments like that usually follow a scenario where an architect proposed, recommended, or demanded a particular solution, only to be overridden by a business decision.
We've all been there, and know the feeling. First things first; as an architect don't put yourself in a position where you can lose. That doesn't mean you can't stake a position, or demonstrate conviction. You just don't want to say "No", rather you want to say "There are risks/costs/concerns" with the solution, that my approach addresses." (This implies, of course, that you have a viable solution for anything to which you might say "No").
Secondly, put yourself in the position of the CIO/CTO/CEO and image two of your brightest people have come to you with differing opinions. One, a business manager is saying "I need to do 'X' to advance my business" (with some implication of a technology that is inconsistent with EA's goals/vision). The other bright person (you?) says to the CxO, that the proposed solution 'X' is inconsistent with stated goals, is technically inferior, and will ultimately cost more and perform less.
Now of the two of you, only one is offering increased revenue, market share, penetration, or other goal which is likely tied to an incentive package. I'm not suggesting that the CxO's motives are anything other than pure, and in the best interest of the company. Rather, the business goals are typically incented and aligned with customer and shareholder expectations. You can count on the CxO to support the business every time.
The power of the EA group will ultimately derive from the EA message, which should be aligned with customer and shareholder objectives and expectations. You will begin to win support of your business units/customer before ever talking to the CxO when your message of EA value is expressed in terms which support the business goals. Asking the CxO to overrule a business decision in favor of an EA recommendation is a bad move; the conflict should never reach his/her desk.