R: index() can not return desired class - r

Question

I have the following xts object with indexClass "Date". index(data) gives me "POSIXct" object. I thought index(Data) will return an "Date" object.
How can I get "Date" object from index()?
str(data)
An ‘xts’ object from 2007-01-15 to 2012-04-27 containing:
Data: num [1:1282, 1:5] 1881 2003 2064 2026 2098 ...
- attr(*, "dimnames")=List of 2
..$ : NULL
..$ : chr [1:5] "open" "high" "low" "close" ...
Indexed by objects of class: [Date] TZ: GMT
xts Attributes:
List of 2
$ tclass: chr "Date"
$ tzone : chr "GMT"
indexClass(data)
"Date"
str(index(data))
Class 'POSIXct' atomic [1:1282] 1.17e+09 1.17e+09 1.17e+09 1.17e+09 1.17e+09 ...
..- attr(*, "tzone")= chr "GMT"
..- attr(*, "tclass")= chr "Date"

Answer 1

Quick answer: Dates don't have timezones. So it (I presume) has to wrap your Date in a POSIXct to preserve the timezone information.
Here is an example without timezones, where it shows the behaviour you expect:
x=xts(1:10, seq.Date(as.Date('2012-01-01'),by=1,length.out=10))
indexClass(x)
# [1] "Date"
index(x)
# "2012-01-01" "2012-01-02" "2012-01-03" "2012-01-04" "2012-01-05" "2012-01-06" "2012-01-07" "2012-01-08" "2012-01-09" "2012-01-10"
str(index(x))
# Date[1:10], format: "2012-01-01" "2012-01-02" "2012-01-03" "2012-01-04" "2012-01-05" "2012-01-06" "2012-01-07" "2012-01-08" "2012-01-09" "2012-01-10"
UPDATE: Adding the tzone attribute to the xts object does not change anything:
x=xts(1:10, seq.Date(as.Date('2012-01-01'),by=1,length.out=10), tzone="GMT")
str(index(x))
# Date[1:10], format: "2012-01-01" "2012-01-02" "2012-01-03" "2012-01-04" "2012-01-05" "2012-01-06" "2012-01-07" "2012-01-08" "2012-01-09" "2012-01-10"
This is despite str(x) giving the same output as you:
An ‘xts’ object from 2012-01-01 to 2012-01-10 containing:
Data: int [1:10, 1] 1 2 3 4 5 6 7 8 9 10
Indexed by objects of class: [Date] TZ: GMT
xts Attributes:
List of 2
$ tclass: chr "Date"
$ tzone : chr "GMT"