Sure [@Necroes], against bullets space marines superior reflexes isn't the best. That's why they wear power armour.

But i wasn't comparing to eldar or lasgun fire, i was comparing to an Ogryn.
And ogryns sure as heck can't dodge incoming lasfire. Nor would they dodge and parry as much in a melee, relying on their superhuman resilience to outlast their opponent.

And, while i don't like using tabletop rules for things. Eldar usually weighed in on initiative 5. At times 4.
Marines have a flat Ini 4 unless they are even more impressive.
A standard human is at 3.
Does the Ogryn even have 3? I'm fairly certain it is 2.

Initiative being the general quick thinking, reaction time and speed of the individual.
In dark heresy, ogryns have a poor intelligence and agility stat. Agility being speed, agility (duh) and it is used in determining turn order in combat.
Space marines have a better initiative. By far.
Eldar have unnatural agility, which gives them sick bonuses.

So checking out some ogryn stats in dark heresy (which is the source i use for most of my comparisons, since the game holds a high production value and is more close to lore that the tabletop), space marines are roughly double as agile than an ogryn.
But they do tend to have more general toughness and strength. Making them better at such tests.
But space marines have unnatural strength and toughness, giving them sick bonuses in those stats.

Also, necron warriors can't phase out to dodge individual attacks. Some more important necrons could probably do that with some impressive gadget, but generally it's a no.
Necrons usually don't have good reaction time either. They are just built out of weird materials. Damn soaky materials.