Interesting... You never dd data to a USB3 disk or SSD? The default buffer size for dd on OS X is also 512 bytes. I've been using `bs=1m` on OS X for ages.
dd is designed to copy raw block data across devices.
Sure, you can abuse both for either purpose, but seems rather misguided to call it out explicitly. What did you intend to gain by doing it?
dd is also designed to copy data from one file to another, in blocks, with optional conversion of the data (eg, from EBCDIC to ASCII), and with optional offsets/limits to copy regions of a file.
dd is not designed to copy raw block data, it is merely a different file copy tool.
dd is for transform-and-copy, so you're abusing dd when writing disk ISOs. The fact that most of the Internet is wrong doesn't make you any less wrong.
"dd is not a disk writing tool" http://www.vidarholen.net/contents/blog/?p=479