Nope, it doesn't. You get what you slot.
But 10% isn't actually shown as 10%. If it's a moderate regen bonus then they are clumped together and will only show the actual HP regen, not the regen bonus.
So lets imagine that 10% were 0.20 HP per second and under moderate regen bonus, with two 10% what you'd see would be 0.40 HP per second : Moderate regen bonus.
Ive taken screen shots that will probably better explain what Ive written.
Regen issues
So, I have two regen bonuses from two sets which give the same %, but Im geting 2 different % in the combat attributes.
Kanto2 is correct, he hasn't missunderstood you.
The "Large improved regeneration bonus". Is the total of all your large (+10%) bonuses. Base regeneration = 0.42%. 10% = 0.042%. 2 times 10% = 0.08% (to 2 dp).
"Regeneration Increase" is due to some other power, possibly Health, it isn't a set bonus.
I really should do something about this signature.
Think the 10% is from a temp power, which means in 2 days, my regen is gona go down 
thnx 4 quick replys
Does the regen bonus from sets decrease if you have more than 1 bonus at the same % ?
Eg, I have 2 bonuses of 10%, but Im currently getting bonuses on my combat attributes, 10% and 8%.