System files shown is consist of system plus other files ...if you see this in storage check you ll see 1.9 gb in system and remaining in the other section...
More detais..my phone storage on l720 says 2.51 in system plus 336.38 in temporary files which comes to 2.9 gb...same in storage check it shows 1.9 system and 1 gb of other files which again comes down to 2.9...so its like following different accounting systems basically and on any new lumias system files would be of 1.9 gb...just do the math like i did and you ll get the clarity...though i don't know about nl800..
yeah i noticed my System file size slowly increasing. My guess is that it now includes the other storage too, hence the reason it varies for each phone.
Smart move since it doesnt show 'other' anymore, people will perhaps stop cribbing.
edit: from lumia storage check looks like i have 1.3gb of temp files.. well, i had 1.2gb but with the "clean" function it become 1.3 XD hard reset is coming ._.