Your proposal is malleable, so in particular, confidentiality does not hold against a chosen-W' attack, which is the key-wrap analogue of a [chosen-ciphertext attack](http://en.wikipedia.org/wiki/Adaptive_chosen-ciphertext_attack). $\:$ Also, the fact that your
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proposal concatenates s with p suggests that H [can probably be evaluated too quickly](http://crypto.stackexchange.com/q/3196/991).
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Although that may be typical, it shouldn't be, since the time needed to try passwords
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in a known way scales linearly with the time needed to evaluate the password hash.
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[This answer](https://security.stackexchange.com/a/31846) gives some better password-based key derivation functions.

The "best reason that it is better for key wrapping" is that AES is hopefully non-malleable.
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(Note that AES should replace xor, rather than replacing H.)
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