The printer does not spray "drops of thermoplastic," it sprays magic chemicals that either inhibit or promote sintering onto a bed of thermoplastic powder and then uses a big o' incandescent bulb to fuse the powder. This is pretty much the selective inhibition of sintering process, so the magic chemicals are probably just something like salt water and black ink.
Now what does this mean? Well because you have to spray a sintering inhibitor on, you can't recycle as much powder, unless they give you a special powder recycler for removing the inhibitor. Because you're printing out lots of black ink, can't really recycle powder, and HP will lock you into using their cartridges you will be paying out the a$$ for ink and 'toner.'
This is a HUGE development though. If the parts really have the same strength and detailing as those produced with laser sintering, as in even if this machine did not come equipped with color capability, then this has just made a lot of big industrial 3d printers obsolete. Getting rid of the need for laser and nitrogen gas purge system for sintering type machines is HUGE! Even with huge expensive print cartridges it's going to be cost competitive with everything out there.
Heck, it probably makes the whole 3d printing service bureau business model obsolete, because this puts high quality 3d printers in the cost range for small businesses.
This is probably the "attack of the killer micros" moment for the additive manufacturing industry.