"In" vs. "out of" [closed]

Why does out require an additional preposition in many cases that in does not?

For example:

I am in town this weekend. Next weekend I will be out of town.

When the lifeguard blows the whistle, everyone must get out of the water. When he blows it again, you may get back in the water.

I am in the office. At noon I will be out to lunch.

One wouldn't say "I will be out town" or "get out the water". There are also some cases where you would say "I will be in to town" or "get back in to the water", but omitting the preposition is also perfectly acceptable.

Other positional prepositions tend to require an additional preposition as well, but not "in". You go down to the river, over to the next county, up to the 15th floor and off to the races.

Why is "in" different?

Out of is a complex preposition and merits its own entry in the OED (Oxford English Dictionary), separate from the entry for out. It has numerous uses, but in your first two examples it means the opposite of in. In your third example, the use of to is rather different, and not really relevant to the main question.

Out of has a long history, but this extract from the OED’s etymological note may help to answer your question more fully:

The history of out of is partly parallel to that of in to, with the differences that the latter is now written into as one word, and that out of is the opposite, not only of into, but also of the static in. One reason why out of has not needed to be written as one word may be that the distinction now made between into and in to is in the case of out expressed by out of and out from: thus ‘they came in to me, into my house’, ‘he went out from me, out of my house’.

There has been discussion in the comments on another answer about the use of out followed immediately by a noun phrase. Out is used in this way with two main meanings. The first (1) is ‘from within, away from’, as in this 1992 citation from Toronto’s ‘Globe and Mail’:

When you become useless, you're out the door.

The OED describes this use as being formerly poetical and now regional and nonstandard.

The second main meaning (2) is ‘outside, beyond’, as in this 1977 citation from J P Donleavy:

A thrush chirping its evening song in the first darkness just out the window.

The OED describes this use merely ‘now nonstandard’. This 1991 citation seems to me to confirm this view:

He spent too much time boozing down the pub. Too much time out the house.

It may be that out + noun phrase is Standard American English in sense (1), but nonstandard, as in British English, in sense (2).

EDIT:

Research in 1997 into the use of out the door and out the window, reported in ‘The Cambridge Guide to English Usage’, ‘found ample evidence of their use in spoken discourse and in published fiction, though this doesn’t yet guarantee their place in British written style generally.’

This is because "out" here is not a preposition, it's an adverb. According to the OED's entry OUT, prep., "out" is no longer used as a preposition in Standard English, though it is in widespread use in nonstandard and regional varieties, and it is apparently now seen as a standard use in American English. For example, in American English you might hear

I took it out the closet

whereas in most varieties of British English we would say "I took it out of the closet".

The other examples you give are also all adverbs followed by prepositions, not two prepositions linked together. "Down", "up", "over", and "off" can all be prepositions in standard English, but not with the same meanings as they have in the examples you quote. For example, "I went over the river" (over is a preposition) is different in meaning from "I went over to the river" (over is an adverb). However, as with "out", you may see them in non-standard varieties being used prepositionally with the same sense as the adverb-preposition construction. For example, my grandmother would have said

I went down my friend's house

meaning the same thing as

I went down to my friend's house.

So, in summary, "out" requires "of" because it is not functioning as a preposition, but as an adverb, and therefore cannot take an object. "In" is a preposition, and therefore can take an object.

Edit: see also Barrie's answer, where he points out that the combination "out of" functions as a kind of compound preposition - it has a single meaning which is based on the meanings of the adverb and the preposition.