Depends on whether you're watching "on demand", or a live broadcast/recording.

I have YouTube TV and when you load up a recorded show, it will let you choose whether to watch the on demand or broadcast version. The broadcast version has more ads, but can be fast-forwarded. The on-demand version has fewer ads, but you can't skip through them.

Really that's the same as on-demand vs live/DVR on Comcast or FIOS, in my experience.

Another possible difference is that cable companies do have the ability to insert their own ads during certain portions of a commercial break. You might notice this if you're watching a national channel but suddenly see an ad for some local business, that's probably inserted by your cable operator.

It's called Local Insertion.

Local commercial (and some non-commercial) broadcast television stations also insert local commercial breaks during programming each half-hour while network-supplied or syndicated content is being broadcast. Television networks and syndication distributors give their affiliates either 60, 90 or 120 seconds each half-hour (typically totaling about four minutes per hour) to run local station breaks, including promos for the station and advertisements for national and local area businesses (and on a few stations, local news updates – which were particularly common during the 1970s through the 1990s, especially as the "24 Hour News Source" format became commonplace in the United States during the latter decade – current time and temperature information, or a brief local weather forecast), over network programming. Typically, these networks air a blank feed showing the network's logo (such as with Fox, NBC and The CW) or a series of public service announcements (as with ABC and CBS), while stations air local commercials.