Er..no, it's exactly the same - 50%.
Except that it's not....
If you set down and roll a D10 20 times & give yourself a point every time it's a 6 or better, you'll end up with more points that if you sat down with a D6 and gave yourself a point every time it was a 4 or better.
I'm sure there's someone that can explain it better, but it does happen that way most of the time.
It's because on a D6 there's only 3 sides that can result in a point for you. On a D10 there's 5. And for some strange reason that makes it easier despite there being 5 sides that won't get you a point.
I'll try and get in here before VoodooMike rips you a new one, but this is basic maths.
Take a d6, and you want a 4+.
1, 2 and 3 are fails (3 results out of 6 = 1 out of 2)
4, 5 and 6 pass (3 results out of 6 = 1 out of 2)
Take a D10 and you want a 6+
1-5 are fails (5 results out of 10 = 1 out of 2)
6-10 are passes (5 out of 10 = 1 out of 2)
They are exactly the same - 50% chance.
You could even take a coin (D2)
Tails fail (1 result out of 2)
Heads pass (1 result of out 2)
The only "strange reason" is your failure to grasp basic probability.