Yes, this is still true.
I've always wondered about upgrading in general.
There are two fundamentally different ways of thinking about it:
1) The upgrading system is completely random (or as "random" as the pseudo-random numbers that are generated by the server can get).
This means that every time one tries to upgrade +7 -> +8, it will be a 10% success rate. This doesn't mean that if you save up 10 items and upgrade all 10 that you will be guaranteed at least one successful upgrade. Like another person said above, one could burn a million in a row or successfully upgrade a million times in a row.
2) The algorithm that defines each upgrade has at least one dependent variable.
This means that some variable about your character (or the environment) is input into the function that determines whether or not an upgrade is successful.
Possible environment variables include: time of day, month of year, premium level, character level, last upgrade success rate (this is where all the faith in the superstitions about "burning" items arise), NPs, items the character is wearing, etc. You get the picture.
I'm sure a lot of little "studies" have been done. Maybe the experimenters recorded their data and posted it somewhere?
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