I really think riot should give us a proper definition of "Critical Strikes"

What exactly am I talking about you say? Well let me give you the scenario here.

Most ADC's will stack items that give "Critical Strike chance" or the chance that their next strike will do double damage to their target. Sounds simple right? Well there are 3 particular instances where things get confusing.

When Anivia hits an enemy with her E while the enemy has recently been hit by either her Q or R, the enemy is dealt Double Damage.

When Karthus hits a SINGLE enemy with his Q ability, the enemy takes double damage.

When Soraka hits an enemy with the Center of her Q, the target takes %50 more damage

These 3 instances of damage are somewhat considered "Critical Strike" damage. and I'm saying somewhat for a couple reasons.

it's considered a Critical Strike when it's applied to a target with Randuin's Omen, which blocks %10 of all Critical Strike damage, which has been confirmed by Riot to be a working thing.

It's also NOT considered a critical strike when either the item Infinity Edge or the mastery Warlord's Bloodlust is involved. Infinity Edge gives Critical Strikes a %50 damage increase, and Warlord's Bloodlust makes Critical Strikes give %15 of the damage back as health and gives %20 attack speed. Granted, nobody in their right mind would build IE or have Warlord's Bloodlust on either Karthus or Anivia, but it still begs the following Question:

If Karthus's Isolated Q, Anivia's Q/R + E combo, and the center of Soraka's Q ARE considered Critical Strike damage, then why doesn't Infinity Edge or Warlord's Bloodlust give the benefits? And if they're NOT considered Critical Strike Damage, why do they get blocked by Randuin's omen?

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