Processing wav files in MATLAB: wavread(), downsampling and PCM as signed vs unsigned

I have used wavread and wavwrite functions to work with wav files. I have some questions about it.

1) Why does reading a wav file generate floating point values for the samples, when actual samples are stored as 8 or 16 bit integers as PCM?

2) why does the wav file header contain a mix of little and big endian format data? certainly the data must in a single format either only little endian or only big endian.

3) Why does MATLAB ignore almost everything in the header from the wav file and only stores sampling rate and actual samples into memory variables?

4) How does one carry out upsampling or downsampling of a wav file?

5) What is the difference between storing audio as signed or unsigned samples in a wav file i.e can the same sound be expressed using both formats?