So, the whole bitshares concept could have been done on the NXT blockchain using NXT as the store of value and creating a bitUSD asset. (I assume they didn't cause the devs could create BTSX's for free.)
Probably but there are a lot of differences still, Bitshare use DPOS you have a transaction speed of 10 sec. You have the delegates,you have dividends that are payde to shareholders etc.
"the hole bitshare concept" - Bitshare X is the first DAC the first of many to come that are using bitshare toolkit : Bitshare Dns, Bitshare Music, Bitshare Play, follow my Vote etc. My point is Bitshare concept is much more then Bitshare X so there are more differences that you can see at first glance.