I absolutely agree with you there. I've been bewildered over this "new" movement also. I think the big difference between an RV and a tiny house is, tiny houses are mostly stick-built, wood and nails, very indiviudalized. RV are still mass produced.
Another thing that grabbed my attention about "tiny houses" is the creative use of storage space. RV's don't utilize very many "smarts" when it comes to utilizing every inch of available space. RV have a LOT of dead space never used, covered over, and hidden.
Also, RV are designed to "move" on the road. Tiny houses, although are designed to (sometimes) move, most do not.
It still blows me away that those tiny houses sell for UP from $100,000! Astounding! Simply crazy in my opinion. But, if it makes someone happy, I suppose that's all that matters.
Give this a few more years and the "fad" will come to an end. They will be wanting to move back to their McMansions and they won't be able to sell their tiny houses, because the market will not want it any more .... BUT ...
RV's will continue on! Rock on RVers!