Torture tests: what do they mean?

[jebem]

I can't resist myself to point out one more situation here.
How powerful hardware can be limited by the software design choices.

Today I have done two very simple tests, published everywhere, on 3 of very popular calculators among us:

Test 1:
(sqrt(6)^2)-6
So, the expected precise result should be Zero, right?

- On a WP-34S super precise RPN calculator (at max. mant. Fix 11): 0,00000000000
- On a Casio FX-991DE PLUS (at max. mant. Fix 9): 0,000000000
- What about a HP-50G: -0.00000000002
- And now the HP-Prime: -0.00000000002

Test 2:
(10^15 + 7.2 − 10^15) * 100
The expected result should be 720.

- On a WP-34S super precise RPN calculator (at max. mant. Fix 11): 720
- On a Casio FX-991DE PLUS (at max. mant. Fix 9): 0,000000000
- What about a HP-50G: 0
- And now the HP-Prime: 0

Go figure.
Do we have here at least two different schools of algorithms, or is it just a matter of limited number of internal digits on HP machines?

I see a similar behavior between the Prime and the 50G in so many situations that I guess HP have just ported the 50G algorithms. That would explain the apparent lack of precision for such a modern and powerful hardware sported on the Prime.

I know all the story about precision/accuracy and number of internal digits, and that the HP-Prime answer is correct for what it can handle, but the fact that it can't give a more precise answer than the other two machines (and the Casio costs less than 30 Euro) put me off a little with my beloved Prime.

My reasoning here is:
- If a low cost Casio can pass Test 1 with flying colors;
- When a moderate cost WP-34S, using much more limited hardware resources than the Prime, can handle much larger internal digits in order to give those two precise answers, why does the Prime sports such a apparent limited precision?
It is not for hardware limitations, I hope!