In this case
And Then There Were None, like a number of classics, has entered the public domain; any old company can, (and has) pick it up, possibly copied it from a TV broadcast and slapped it on disc. Image and VCI are among the better companies when it comes to giving films of this nature decent treatment (they at least try and find film elements that haven't been dragged through a hedge backwards) but it's very rare to find anything approaching the quality found when a decent studio unearths original elements from its vaults and sets about a transfer.
While a studio may still own good elements of a PD film, they may be reluctant to produce their own version after all the commercial 'juice' has been sucked out of it. (Thankfully, Paramount gambled successfully to produce a superb DVD of the much copied
McLintock!)
The same sad state of affairs afflicts a film with a similar plot;
The Cat and The Canary. It's a crying shame.
But why is R1 superior? Well, they aren't every time (and I won't go into the whole PAL speedup, NTSC/PAL debate here), but in general, R1 releases seem to have that little bit extra, be it a slightly better transfer, better art, better sound (space reasons allied to a couldn't care less attitude means that less R2 discs have an original mono sound option), better extras. Use Rewind to check out differences on discs you fancy, or just ask here - I'm sure someone will help.
Linear Mode
