I'll step in and say that I think every single movie being questioned is horror (of those I've seen that is), and that if we say a lot of those aren't horror then we're really limiting what horror can be.
I would then like a list of which of the films in question you've seen. Especially since by the logic of your argument we should also call all of these films comedies and romance. This isn't 'Nam. There are rules.
There are movies that I wouldn't call a horror movie, none of them happen to be on that list. The logic of my argument is that people seem to be saying, "that film has a lot of comedy elements, it's not really a horror film." Or, basically, that if a film isn't trying to be scary then it's not horror, which I find immensely limiting. And, from the list of films that others are questioning I've seen,
Bad Taste
M
Saw (James Wan, 2004) 4
28 Weeks Later (Juan Carlos Fresnadillo, 2007) 9
Misery (Rob Reiner, 1990) 8
May (Lucky McKee, 2002) 6
Species (Roger Donaldson, 1995) 5
Signs (M. Night Shyamalan, 2002) 7
Timecrimes (Nacho Vigalondo, 2007) 4
Arachnophobia (Frank Marshall, 1990) 8
Anaconda (Luis Llosa, 1997) 6
Event Horizon (Paul W.S. Anderson, 1997) 7
Dawn of the Dead (Zack Snyder, 2004) 10
Invasion of the Body Snatchers (Philip Kaufman, 1978) 6
One Hour Photo (Mark Romanek, 2002) 7
Transsiberian (Brad Anderson, 2008) 8
Splice (Vincenzo Natali, 2009) 5
Let Me In (Matt Reeves, 2010) 6
Near Dark (Kathryn Bigelow, 1987) 6
The Mummy (Stephen Sommers, 1999) 7
Pitch Black (David Twohy, 2000) 7
Lake Placid (Steve Miner, 1999) 5
Ghostbusters II (Ivan Reitman, 1989) 8
Final Destination (James Wong, 2000) 7
Frailty (Bill Paxton, 2001) 6
Final Destination 2 (David R. Ellis, 2003) 7
Hard Candy (David Slade, 2005) 7
Cloverfield (Matt Reeves, 2008) 8
Deep Blue Sea (Renny Harlin, 1999) 7
Eight Legged Freaks (Ellory Elkayem, 2002) 4
Bubba Ho-Tep (Don Coscarelli, 2002) 2
Dead Calm (Phillip Noyce, 1989) 9
The Addams Family (Barry Sonnenfeld, 1991) 6
Alien³ (David Fincher, 1992) 5
Cube (Vincenzo Natali, 1997) 9
What Ever Happened to Baby Jane? (Robert Aldrich, 1962) 3
Sphere (Barry Levinson, 1998) 6
Zombieland (Ruben Fleischer, 2009) 8
Tucker and Dale vs Evil (Eli Craig, 2010) 5
Beetlejuice (Tim Burton, 1988) 8
The Act of Seeing with One's Own Eyes (Stan Brakhage, 1971)
Barton Fink (Joel Coen, Ethan Coen, 1991)
Beetlejuice (Tim Burton, 1988)
Blue Velvet (David Lynch, 1986)
A Clockwork Orange (Stanley Kubrick, 1971)
Dr. Mabuse: The Gambler (Fritz Lang, 1922)
Dressed to Kill (Brian De Palma, 1980)
The Elephant Man (David Lynch, 1980)
Eyes Wide Shut (Stanley Kubrick, 1999)
Fanny and Alexander (Ingmar Bergman, 1982)
Fantasia (Ben Sharpsteen, 1940)
Irreversible (Gaspar Noι, 2002)
Meshes of the Afternoon (Maya Deren, Alexander Hammid, 1943)
Mulholland Dr. (David Lynch, 2001) - scary moments, but not a horror film.
The Nightmare Before Christmas (Henry Selick, 1993)
Paprika (Satoshi Kon, 2006)
Picnic at Hanging Rock (Peter Weir, 1975)
Pirates of the Caribbean: The Curse of the Black Pearl (Gore Verbinski, 2003)
The Prestige (Christopher Nolan, 2006)
Salς, or the 120 Days of Sodom (Pier Paolo Pasolini, 1975)
The Seventh Seal (Ingmar Bergman, 1957)
Shutter Island (Martin Scorsese, 2010)
Strangers on a Train (Alfred Hitchcock, 1951)
Take Shelter (Jeff Nichols, 2011)
The Terminator (James Cameron, 1984)
Terminator 2: Judgment Day (James Cameron, 1991)
United 93 (Paul Greengrass, 2006)
And every one of these I would quantify as a horror movie.