That is the big difference between Zigbee and Z-Wave. Z-Wave is pretty much Z-Wave with one company and its licensee(s) producing chips, so all Z-Wave devices should have no problem communicating to each other. Zigbee is an open standard with many companies producing chips, supporting many different industries. Unless the "profiles" match, then things don't connect together. I believe that the Lowes system uses a proprietary profile, preventing it from working with other things. That was by their design.
You might think Z-Wave interconnectivity is a good thing, as you can "rebrand" devices for your benefit, as mbreeden said, but this can come back to bite companies as well. I remember a few years ago, Simply Automated, which was selling $75 UPB switches that professional installers generally installed, got the bright idea, to increase sales, it would sell a DIY home automation system with DIY UPB switches that would sell for the DIY price of around $35 each at Frys Electronics. Different customers, different price points. Well it didn't take long for customers that had been buying the $75 UPB switches from dealers to realize they could buy the same switches for half price at Frys.
People, including me, swamped Fry's and bought all the switches we could, while home automation dealers got quite upset that their customers were buying switches from Frys for cheaper than they were buying them for from Simply Automated. Dealers got mad. Simply Automated realized their mistake then discontinued the Frys product. The funny part was after that, Frys slashed the prices on these switches even more to get rid of them, which caused another feeding frenzy. I have maybe 15 of these switches and they have worked well.
I'm not sure how the Lowes devices were priced, and Z-wave is a bit more of a DIY standard to start with, but you may want to buy all the Lowes Z-wave devices while you still can.