I'm flying to Asia in the summer and I noticed a long list of special diets that are available. In Europe, I have always been able to order a cheese sandwich instead of one that contains meat. Is that the case everywhere, or are there airlines that don't serve vegetarian meals?
Airlines provide a wide range of meals for people with different dietary restrictions. They have a common set of meal codes that they use so if you've wondered what the strange 4 letter code is on your ticket, it's one of these if it's vegetarian (there are other codes for non-vegetarian meals such as low-sodium that I won't list here but you can click on this link to see):
VGML is a vegan meal
VLML is a traditional western vegetarian meal that won't contain meat or fish but may contain eggs
AVML is a traditional asian vegetarian meal, no meat, fish or eggs and in an asian style
VOML is a vegan meal in a more oriental style
VJML is a Jain meal, vegan but with additional restrictions such as no aubergines (eggplants), onions, garlic and potatoes and other Jain based restrictions
RVML is a raw vegetarian meal, and
FPML is a fruit platter meal
Not all airlines serve all of these on all flights but you can always order a meal that's more restrictive than you normally are. Some of my non-vegetarian friends order vegan meals on airlines just because they find them more palatable. What airlines do offer probably also depends on what routes and therefore passengers they fly. The happy cow has a list containing information about many major airlines.
Airlines attention to detail has not always been the best in the past either, I've been offered VGML (vegan) meals where the main meal itself was vegan but the desert offered contained dairy, and even on more than one occasion gelatine, and the creamer has been dairy too on occasion when it should not have been. Having said that things do seem to be improving from my, admittedly anecdotal perspective.
This doesn't exactly answer "are there airlines that don't serve vegetarian meals", however you are likely to find more vegetarian options on Asian airlines. Given the number of Hindus and Buddhists that travel, it is essential.
Failing that, take your own cheese sandwiches :o)
Check out this answer for more info on religions that require vegetarianism.
On long flights I always request the Hindu option (if possible).
But I would highly recommend just bringing your own food if the Hindu is not available. The food is not great tasting, and is often junk. If you are coming from home, you can homemade sandwiches, wraps, sushi, and nuts(!), for example.