In the days before feed concentrates large herds of cattle, sheep or horses could only be maintained by moving them from pasture to pasture on a seasonal or yearly basis, ie. transhumance, or perhaps semi-nomadism. The movements need not, if the pasturage was of reasonable quality, have covered huge distances. Indeed a particular herd could have been centred on a single fixed settlement where a proportion of the stock could be over-wintered. This type of economy would still have entailed that a proportion of the adult male population move with the herds and therby ensure that horsemanship and horse-ownership would be at a premium. As regards permanent settlements of reasonable size and nomadic societies.
History shows that the two are by no means mutually exclusive.
The Mongols in the time of the successors of Genghis had Karakorum as a capital. Further, that the presence of fixed settlements of varying size does not preclude this type of society. The question I had promised to address was whether the Rohirrim were nomadic. A formal, concise, and logically presented argument would require days of work to prepare. I've looked back through my Usenet discussions on the issue and I see where I have dealt with many tangential issues in the course of those discussions.