Yes - I have purchased with cash.
Some I bought using exercised stock options. The rest I purchased when we bought a new house - we had previously owned outright but financed our new primary residence at 3% (15 years) so I could get more cash to buy houses yielding 9%+.
The numbers say you can often get a much better return using leverage but for me I had the cash available and I viewed the alternative uses of my cash (stocks, bonds, MM) as less attractive considering how cheap real estate was 3-4 years ago when I started buying. Also, in theory I could have purchased 4x the number of places if I had paid only 25% down but in reality I would have had issues finding that many deals, managing that many properties (I self manage) and would have run into lending problems trying to actually get regular loans once I got past 4-10 places.