You have things reversed!

Nikon traditionally always put their motors in the bodies, offering supplementary lens mounted motors for additional performance on some high end tele lenses only.

To be able to compete with the very low end Canon bodies on price (which is the only thing most purchasers for that category consider when making a purchase) they decided a few years ago to introduce a few bodies without body mounted motors, and at the same time introduce a line of low end consumer grade lenses with lens mounted motors, primarily for use on those bodies (the D3000 and D5000 I believe were the first).

Canon has always (well, since the introduction of their EF lens mount back in (I believe) the late 1980s had all their motors in the lenses only, never in the body.

This of course increases the price of lenses, especially for people buying more than one lens, as now you have to buy a lens motor for every single lens (for that reason 3rd party lenses for Canon had often been slightly more expensive than the otherwise same lens for Nikon).

Both systems have their advantages. Having the motor in the body allows for simpler lenses, puts weight nearer the photographer, and reduces the system cost and weight for people having many lenses. Having the motors in the lens allows motors which are designed specifically for each lens, potentially allowing for lower power, cheaper, motors for smaller lenses (the motor in a Nikon D200 has to be able to power both a lightweight 50mm f/1.8 D and a very heavy 600mm f/2.8 D (which existed or was planned at the time, now the 600mm is only available as AF-S, with its own complementary motor).

The main thing you'll experience when buying a D5100 is that you won't have full choice of all F mount lenses, unless you are happy with manual focus on them. But probably, by the time that becomes a limitation, you'll be looking at buying a bigger body anyway, and no longer have that problem.