Offices, yes, but offices for things like lawyers or accountants or maybe dentists or barbers—the sorts of offices that normal people would visit on a regular basis. They're not retail, but they're still in the overarching "personal services" category of businesses. Banks also fall into that category (as long as they're branches and not just bank office buildings).
Those sorts of businesses need to be clustered together because they depend on mutual business for their success. For example, restaurants do well when they are near movie theaters (particularly if they have pizza by the slice and other quick food) because kids want to grab something quick to eat before (or after) seeing a movie. Downtowns work when their businesses complement one another.
Tech firms don't belong in the core part of the downtown for the same reason that manufacturing plants don't belong there. Non-employees don't go downtown to visit a Google or Apple or Cisco office. Those sorts of offices should be within a reasonable distance from at least some services (particularly food) because that makes life easier for the workers, but such businesses can easily be a few blocks removed from the main strip without adversely affecting the success of the business. And if they start using space that would normally be used by retail and personal services businesses, they start to adversely affect those other businesses, eventually leading to the total collapse of the downtown area.