Stim, VERY GOOD!!

It is pretty well recognized that 440 has been standardized as being 'A', however Stim's post may be enlightening for those who are concerned with wish to utilize the numbers that are mathematically consistent with the speed of light..(well done!)...That being said, the expression that I was referring to, about 'purists being out of tune', was aimed at those snobby folks who were too arrogant to either use a 'tuner' or deluded themselves into thinking that they had 'perfect pitch'..and consequently, weren't even properly in tune with themselves!..let alone any other accompanying instruments!!
One thing that musicians should be aware of and discipline themselves about,i s getting used to 'hearing' themselves being out of tune..but getting used to it!...it's much like making a recording, with errors, listening to the recording over and over, and getting used to the errors and writing it off...It's the same lazy process, and really makes an ass of the player...when he THINKS it was 'just great'!
Even if you use a digital tuner to 'lock in' what the frequencies really are, rather than what you THINK you've been accustomed to hearing, use them long enough to get accustomed to the absolute correct tuning. You may fine your ear has some adjusting to do. Remember, your listening audience may not feel like making excuses to themselves as to why it sounds 'OK, when it really isn't....they'll just give you a polite BS 'compliment' and move on to whatever conversation someone else wishes to engage in, without giving you a second thought.
AND, if you sing, for God's sakes, study!

GfS