I have three files,
blk0001.dat 2,097,361,271 bytes,
blk0002.dat 2,097,295,438 bytes, and
blk0003.dat 1,249,842,320 bytes.
Are these three files the same for everyone? Or a crisper question might be, are blk001.dat and blk002.dat the same for everyone who is synchronized?
Depending on how orphan blocks were received from the network and how data was reorganized on the hard drive, different users will have different checksums of blockchain files, although the contents are essentially the same. The most recent file, blk0003.dat will be changing in size every time a block is received. Data for downloadable blockchain distributions such as in this thread is specially prepared to be an efficient in-order set of blocks and to be verifiable by others.