Anglophilia is not uncommon in American audiences. It's almost the basis for the British film industry. The success of any Richard Curtis movie can be explained away by the fascination American audiences have with British systems, British history, and the vaguely romantic, mythological air that pervades the entire country... apparently.
For five years, Downton Abbey has been providing that anglophilic fix, but all that will come to an end with Downton Abbey Season 6 being the last in the series. How has Downton managed to maintain it's position as the premiere not too trashy not too snooty period piece that viewers can't get enough of? Well, by doing just that. Downton Abbey has maintained its dominance by having the trappings of a prestige period drama, while secretly indulging the more base desires that the audience look for.
Downton Abbey may present a refined image of early 20th century England, but it carries over into Season 6 stories of murder, illegitimate children and family feuds. That's an okay thing. It's what kept Downton Abbey going so long, but what will be there to fill the same space when Season 6 is done?
I certainly won't try to equate Outlander with Downton Abbey. They're vastly different products when you actually inspect them. Not just because one is set in the 18th century and the other in the 20th. WHATEVER IT'S ALL HISTORY! It does seem, however, that both these shows provide similar pleasures. Outlander is the story of Claire Beauchamp becoming embroiled in the war between the Redcoats and Highlanders, with her able to adopt fully the role of a lady of the time, yet have her contemporary values conflict with the romantic allure of history, just like the audience! Ignore the part with the time travel. Downton Abbey doesn't have that... YET! Who knows how Season 6 will end?
Outlander's appeal is a little more gendered than Downton's. Not meaning to conflate entire demographics, but the idea of being whisked away by strapping men of a simpler time, and love being the one thing that ties you to history, is a staple of women's pulp fiction. Outlander would be welcome on a bookshelf, and is incidentally where the show itself is adapted from.
Downton Abbey and Outlander are also both shows which tout the romanticism of history while exhibiting the inequality that runs through it. The Early 20th, and mid 18th centuries weren't the most accommodating times for women, so any emergence of self guided narrative and triumph resonates much clearer with the audience than if the show was set in modern times. Outlander looks set to fill the Downton-shaped hole after Season 6, but there's one issue for fans of British TV.
Outlander isn't entirely British
While Left Bank Pictures is an English production company, facilitating shoots that take place on on the British Isles, Outlander was adapted by American screenwriters for the American "Starz" (we spell it with a z so you don't look too classy) network. One could easily be fooled into thinking this was a BBC production, for so often, British production assets are utilised to give a sense of British authenticity that's oh so profitable. Game of Thrones has this issue too, being so British in almost every way aside from the fact it's completely American. Outlander seems to be taking up this mantle of obscuring your show's nationality for the sake of looking good.
This is extremely different from Downton Abbey, which is so English that the script was probably covered in the crumbs of cucumber sandwiches. It's also broadcast on ITV, that one other channel the UK has that isn't the BBC. After Downton Abbey Season 6, it seems we have to wait longer for something from Britain to truly capture the world's attention as Downton did. Unless Season 6 introduces time travel and gets a spin-off. That will definitely work!