I'm sorry, but getting a kill as a support is never a bad thing. Okay you're adc has say 75 farm, the enemy has 100 farm too, their support has no kills no cs, but you have 2 kills as the support. Even though he is behind in CS look what you have. Zeke's herald there is 20 extra AD, and oh look 10% lifesteal that he has as long as he's with you. The enemy support doesn't have this item because he has less gold. You're going to come out on top because you're support is stronger than theirs, and your adc benefits from it. If you can give the ADC the kill yeah do it, but it in no way hurts him not to. I don't get what's so hard to understand about that. I would rather have a Leona as my support with a Warmog's on that can tank the other ADC, and initiate on him over a kill. I don't think people realize how kills aren't important. The important thing is deaths, and deaths hit someone hard. A death at low levels is maybe 2 waves of minions you missed. That's 12-13 CS you don't have, and 12-13 minions worth of exp you lost. That's roughly 240 to 280g in the early game lost, and later game it's more. It's also easily a level lost in early game. Now a kill compared to that is 400g assuming they aren't already feeding because then it gets as low as 80g for a champion. First you have to kill them, second you put yourself in danger of being killed instead, and third you ignore minions by attacking them. Your goal shouldn't be to make money off a champion's death it should be to make it off minions. The risks in killing minions vs jumping on an enemy champion are way different, and at times not worth it. Now if the enemy dies though that's 780g, lane exp, and champion death exp you have over him assuming you kill every minion. If the support gets the kill he gains 400g enough for plenty of wards, and more auras for you. You get 100g for the assist, and then 280g from the free farm. You essentially have a champion kill worth of gold right there, and then you have the extra level so the extra pressure. Now if you get the kill as adc that's roughly 680g you gain, so enough gold for say 10 more AD. Your support gets 100g for the assist enough for 1 ward. If you actually look at it that way the support getting the kill makes your lane stronger, but the adc getting the kill makes your one person stronger. You need about 5 kills for a BF sword because each death decreases the amount of gold they give, so honestly kills don't even matter.
Also I think every ADC should rush an avarice blade early game. It's 3 gp10, and extra gold on every minion/champion kill. It's also crit chance, so even if you have even CS you're in the lead because gp10 and extra bounty on kills.
Oh and about the gp10 seals. It's not worth it all you get is 2gp10 from all of your seals being used up. You already get 3gp10 from quints, and 2 more from masteries. Most I would do is 4 gold seals for one extra gp10 because in a bad situation you're going to need that armor. You're better off being tankier with armor red, and yellow. That or having some extra damage to offer with a penetration red matching your champion.
This post was also much to long. xD
Oh this also explains really well the importance of avoiding a death rather than making sure you get the kill.
http://www.youtube.com/watch?v=Z4cTEpSzZcM