The distinction is that when I ask Steve for prayer, I'm not asking him to do anything other than pray to God on my behalf. I am not asking Steve to act on my supplication to God. Those are very different things. If I thought that Steve was in a position to personally grant me strength (or whatever), then I would just ask him for it. I wouldn't ask him for his prayer to God. If I asked him, and Steve could not give me the wisdom or advice for strength, etc., THEN I would ask him for prayer. Sometimes I might do both, but that would only be when I wanted more than Steve could give me. The point is that you are NOT simply asking for prayer, as has been advertised. You are asking for specific action other than prayer.
If you pray to a Saint for a specific action other than prayer, I'm guessing you think the Saint has the power to grant your request. Therefore, there is no need to "bother" God with it. I see this as problematic for several reasons, one being that it specifically diminishes your dependence on God.
The distinction I had in mind was that Steve praying and Mary praying have a different effect because of what Mary is. It is not a Catholic thing, but if I were, with the Orthodox, say Holy Mary, save me! -- I would still be asking her for a prayer. The difference is that while Steve can pray for my salvation, Mary's prayer has the strength of her being one who made that unique and central contribution to my salvation already.
Also keep in mind that we do ask the saints for things other than prayer. We also ask for guidance. And, of course, we thank them and honor them for their witness.
None of that takes away from Christ. We discussed it before: when I spend time with my children and my parents in law, it take nothing from my love for my wife; rather, it is another expression of my love for her. Likewise with Christ: it is because I love Him, I feel compelled to put myself in the company of His saints and His mother.