The internal market counts as a swap, not a conversion. A conversion will destroy the input token and create the output token. How that affects the market is slightly different.
The peg is most definitely not between SBD and STEEM. The underlying mechanism is the feed price which is how the witnesses determine how SBD is printed and converted.
By the way, high steem prices means more SBD is being printed. Long term there is natural downward pressure on SBD price.
OK, thanks, now I get why "conversions" are spoken of differently to just trading the two currencies internally.