The reason for my post was to understand why people say USBasp is the "standard", when the other VUSB solution is not that solid.
if by standard you mean 99% of hobbyists use usbasp than you are correct. even among arduino users alone usbasp dominates these days. considering other hobbies like rc etc alternatives like ardunio-as-isp, usbtiny, and older hardware are virtually unknown. just like with other methods there are drawbacks:
biggest problem with stock firmware is some older versions generate a warning to upgrade which is incorrectly interpreted as an error by noobs. this often leads to more trouble than it solves. for m2560 it works fine unless your program is bigger than 128kbytes which is unlikely. it does program raw chips ok though.
the o'fischl version requires use of avrdude -B option to program raw chips. usbasp-v1.5.hex" is a version modified from fischl 1.4 by petervh to fix the mega2560 bug. more info here: http://forum.arduino.cc/index.php?topic=363772.0.
bottom line is usbasp works fine for most arduino setups and only less common applications need care. for those odd situations firmware upgrades are available to solve all the problems mentioned.
if i come off as a fanboy its because i am. hard to beat for a dollar and change free shipping. i do recall as recently as couple years ago just mentioning usbasp would bring on tirades about cheap chinese junk from mkII or dragon fans. maybe understandable that someone who spent 10x more might feel need to defend their investment even if drawbacks were obvious. however hard to understand that attitude these days when advantages of the cheapo dongle are well known.
that said if i were going to build from scratch it would be arduino-as-isp. the sketch is quite polished and a lot easier to flash a uno than building usbasp with oddball crystal and wiring. total cost only a few bucks more than usbasp and no wait from china. imo arduino-as-isp is a great fallback if no usbasp available.
ps. recent experience leads me to believe vusb concerns are largely unjustified. if you use a crystal instead of rc and proper software it is trouble free with virtually all pc systems even latest os. i certainly dont encounter compatibility problems with usbasp.