No, that is not true. A proper matte paint job will show hard water spots, and will still need washed and waxed regularly to maintain quality. It still has a clear coat. Hard water will still leave mineral deposits on the clear coat, and will reflect the light, the same as they would in clear coat on a glossy paint car. You may notice them less easily though, as the paint is less reflective, underneath the clear.
An improperly painted matte paint job (without a clear coat), will probably require more maintenance, as any rocks hitting the body on the highway, water, or sap from trees, for example, will directly damage the paint. Fixing that will mean sanding and touching up the area with more paint. Direct water exposure may also cause the paint to run.
Both forms of painting will also be susceptible to UV damage. Wax helps protect against this.
Chemical Guys has several videos on YouTube which discuss protection for matte and other paint types, as a matter of advertising their products. The videos are informative, regardless of which products you use. How to Protect Matte Paint for example, has info and demonstration on a matte black Aston Martin V12 Vantage.