Essentialy, AMD's "X" nomenclature regarding its upcoming Ryzen chips seems to denote the presence or absence of their touted XFR (eXtended Frequency Range) feature. This is part of AMD's SenseMI Technology suite, which aims to bring higher, intelligent performance to their Ryzen chips through the use of some particular technologies. XFR as it is, appears to be an added, automated overclocking capability to the chip, going further than the Precision Boost clocks would usually allow, supposedly scaling with the cooling performance of the end user's machine. This would fall in nicely with the rated TDP's of the non-X processors being rated at 65 W, with the X-branded, XFR-enabled processors featuring a higher theoretical TDP limit in-line with the capabilities of the XFR feature. As such, while it is true that an AMD Ryzen R7 1700 chip would also have base and boost clocks, much like their 1700X counterpart, the 1700's boost capabilities are designed for the chip not to surpass this 65 W hard limit. The 1700X, however, would be able to dynamically overclock according to the environment and cooling efficiency of the end user's rig, thus allowing it to, in some cases, hit a theoretical power consumption peak at the rated 95 W.
This theory (and AMD's strategy) would go some way to explain the high price difference between the 1700X and the 1700 R7 processors, which have a measly 100 MHz difference in their boost clocks favoring the 1700X (3.8 GHz vs 3.7 GHz on the 1700). After all, it still remains up in the air how good of an overclocker will AMD's ZEN architecture be, but a TDP difference of 30 W could go a long way overclocking-wise, especially when you consider AMD can apparently make these chips tick at 3.8 GHz with a measly 65 W TDP for an 8-core, 16-thread chip.