I see you are using your resources well. Smogon is good, even for in-game stuff.
You are right about the Attack thing. Any Salamence, Adamant or Jolly, should be using 252 EVs in it.
With Speed, you kind of have the idea, but you should be asking, why specifically do I use 176? Why not something higher? I use 176 Spe because Adamant Salamence will never outspeed a Max Spe. Pokémon with higher than 90 Base Spe. However, the Base 90s often run a +Atk or SpA nature. Therefore, Salamence should be aiming to outspeed them, because they are the most immediate beatable threat. Assuming that they run 252 Spe EVs, they will all have a Speed stat of 279. 176 Spe EVs give Salamence a Speed stat of 280, meaning that you will never fail to outspeed them. You can't risk running any lower because this will result in a Speed tie, which you have a 50% chance of losing.
The rest is invested in HP for Bulk. Note that, with 80 EVs, Salamence has an odd HP Stat. This is important because it means you can switch into Stealth Rock 4 times and still be alive. If a Pokémon has a weakness to Stealth Rock, and has an Even HP, then 4 EVs should be moved from HP into Def. or SpDef.
Sorry if that was a bit confusing, but it is a decent example of how EVs can be much better used than just 252 / 252 / 4. If an Adamant Salamence was to run the standard Spread, then it would be wasting a good 80 EVs which, if you want to do really well, you can't have.