Star Trek TNG TV episodes on DVD/Netflix different from network/cable telecast?

Yes, DVD versions of shows can often differ--sometimes drastically--from the original broadcast version, as can syndicated broadcasts. Whether they'll include additional material or exclude original material all depends.

Most often, material is cut simply for time on broadcast. In syndication runs, more ad revenue may need to be generated, so more time is cut, or the running time compressed (footage can be speeded up; sometimes inadvertently if video was crossing standards, since NTSC is 30 fps, and PAL is 25 fps). In addition, sometimes content may have been censored by a network but added back in for a "director's cut" version (e.g., Steven Moffatt's Jekyll had three different edits--with different footage/audio [the audio edits were mostly for language] between the original BBC airings, the US airings on BBC America, and the DVD sets). Another possible cause for differences can be linked to licensing issues with DVDs: for example, Keen Eddie lost their rights to some of the music used on the tracks for braodcast, and so the DVD went out with different music choices on the audio tracks.

And do we even need to mention the issues with the HD blu-ray version of Buffy the Vampire Slayer?