Studios that release titles for purchase on only one digital retailer

[Splinterverse]

I recently noticed that most Arrow Video and Blue Underground titles are only available for purchase on iTunes. Some Blue Underground titles can be streamed for free on Vudu, but not purchased.

I prefer to have all of my digital purchases in one place (Vudu), but if the studio won't release there, I'm willing to make exceptions. Do you guys know of any other studios that only release to one digital retailer? If so, which studios/retailers?

EDIT TO ADD:
This is a running list of what has been documented in this thread so far (please keep replying with more info):

==Studios==
Arrow Video (iTunes only)
Blue Underground (iTunes only for purchase, streaming elsewhere)

==Titles==
(For titles, I use this site as well as justwatch.com to confirm the reports)
18 Again! (Vudu and Amazon only)
Bleed (2002) (Amazon only)
Dream Lover (Vudu and AMC on Demand only)
Here Come the Littles (iTunes only)
History of the World: Part 1 (FandangoNow only)
Masters of the Universe (Microsoft Store or Vudu via D2D)
Night of the Comet (Amazon only)
Scrooge (Amazon only)
Smurfs and the Magic Flute (Amazon only)
Tomb of Ligeia (Vudu only)