Just because shows like Drowsy and SA dont fly here does not mean that west end shows are much worse.
SA is a show that divided many people in NY but you have a lot more theatre 'kids' that will keep shows like that open there than we have in the UK, our audiences are a little older.
Saturday Night Fever (awful show) was not considered any bigger hit here in the UK than it was on Broadway. Critics here pretty much dismissed it and it ran for under 2 years and won zero awards, the last 6 months of it run in the UK also was playing to a half empty house. The Broadway production ran for over 500 performances, not much more than the West End production.
Wicked (dreadful)on Broadway will also out run the London production.
The funny thing is that the reason so many new UK musicals fail is because of the American musicals like Wicked and Hairspray which do big business here.
I dont think that the West End musical scene is as strong as it once were (though i think our productions are far better) but its play output is fantastic.
The West End has had a run of bad luck with new musicals over the past few years with Imagine This (heart in the right place but went wrong), Gone With The Wind (snooze fest), Bad Girls (Brilliant and should have run longer), Desperatly Seeking Susan (jukebox musical) etc all failing, yet the revivals its producing far exceed many of the recent misjudged Broadway revivals. The West End has recently produced Sweeney Todd (Went To Broadway), Sunday In The Park (Went To Broadway), La Cage (Plans for Broadway) and so on and so on.
I also think many more musical writers exist in the states whilst many of the theatre writers here in the UK are play orientated.
Like i said earlier, looking at Broadways current line up and the West Ends current line up, neither are glowing.
West End
Ave Q (Broadway Transfer)
Billy Elliot (British Musical)
Calender Girls (British)
Blood Brothers (British Long Running)
Chicago (Broadway Transfer)
Dirty Dancing (Australian naff show)
Grease (American Musical)
Hairspray (American Musical)
Jersey Boys (American Musical)
Joseph (revival)
King and I (Revival)
La Cage (Stunning Revival)
Les Mis (Long Running British Show)
Lion King (American)
Little Night Music (Stunning revival)
Mamma Mia (Urgh)
Oliver (Revival)
Phantom (Long Running)
Priscilla (Oz import)
Sister Act (new musical)
Spring Awakening (flop transfer)
Sunset Blvd (stunning revival)
Thriller (hen night trash)
Tick Tick Boom (nw production)
We Will Rock You (British Jukebox show)
Wicked (the anti christ)
Broadway
9 to 5 (based on a film)
Avenue Q (inovative when it 1st opened)
Billy Elliot (British)
Chicago (Rent a Celeb)
Guys and Dolls (terrible revival, the brits did a better job at reviving an American classic)
Hair (Revival)
Jersey Boys (Jukebox musical)
Mary Poppins (British)
Mamma Mia (British and Jukebox musical)
Rock Of Ages (Jukebox Musical)
Shrek (Based on a film and crap)
Lion King (Disney Spectacle)
Little Mermaid (Dreadful show)
Phantom (British)
West Side Story (Average revival)
Wicked (Less said the better)
In fact looking at the 2 lists i would say that London has more variety right now, even though much of the variety is non UK written
Namo i love u but we get it already....you don't like Madonna