Commodore PET: Choosing a Computer Made Simple

The PET had been around for nearly five years by the time this advert was published, and so it's less of a case of advertising the hardware - which hasn't really changed much, apart from a bigger screen, updated BASIC and more memory - and more of a case of advertising the software available for it, the uses it could be put to, and the support you could get for it. 

Software was perhaps becoming the more important differentiator by now, for instance the release of Visicalc in 1979 had changed the fortunes of the Apple II and effectively saved the company. 

Often sales of machines would live or die by the number and diversity of titles available, and bigger companies like Commodore would invest money (or early on, by encouraging enthusiasts) to write enough of its own to make sure it had all the major applications covered, if they weren't being addressed by third parties.