Why does Browser still sends request for cache-control public with max-age?

Why does Browser still sends request for cache-control public with max-age?

I have Amazon S3 objects, and for each object, I have set
Cache-Control: public, max-age=3600000
That is roughly 41 days.
And I have Amazon CloudFront Distribution set with Minimum TTL also with
3600000.
This is the first request after clearing cache.
GET /1.0.8/web-atoms.js HTTP/1.1
Host: d3bhjcyci8s9i2.cloudfront.net
Connection: keep-alive
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like
Gecko) Chrome/29.0.1547.57 Safari/537.36
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8
And Response is
HTTP/1.1 200 OK
Content-Type: application/x-javascript
Content-Length: 226802
Connection: keep-alive
Date: Wed, 28 Aug 2013 10:37:38 GMT
Cache-Control: public, max-age=3600000
Last-Modified: Wed, 28 Aug 2013 10:36:42 GMT
ETag: "124752e0d85461a16e76fbdef2e84fb9"
Accept-Ranges: bytes
Server: AmazonS3
Age: 342557
Via: 1.0 6eb330235ca3971f6142a5f789cbc988.cloudfront.net (CloudFront)
X-Cache: Hit from cloudfront
X-Amz-Cf-Id: 92Q2uDA4KizhPk4TludKpwP6Q6uEaKRV0ls9P_TIr11c8GQpTuSfhw==
Even while Amazon clearly sends Cache-Control, Chrome still makes second
request instead of reading it from Cache.
GET /1.0.8/web-atoms.js HTTP/1.1
Host: d3bhjcyci8s9i2.cloudfront.net
Connection: keep-alive
Cache-Control: max-age=0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like
Gecko) Chrome/29.0.1547.57 Safari/537.36
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8
If-None-Match: "124752e0d85461a16e76fbdef2e84fb9"
If-Modified-Since: Wed, 28 Aug 2013 10:36:42 GMT
Question: Why does chrome makes second request?
Expires This behavior changes when I put an explicit Expires attribute in
headers. Browser will not send subsequent request for Expires header, but
for cache-control public, it does send it. My all S3 objects will never
change, they are immutable, when we change file, we put them as new object
with new URL.
In Page Script Reference Chrome makes subsequent requests only sometimes,
I did this test by actually typing URL in browser. When script is
referenced by HTML page, for few subsequent requests chrome loads cached
scripts, but once again after sometime, once in a while it does send
request to server. There is no Disk Size issue here, Chrome has sufficient
cache space.
Problem is we get charged for every request, and I want S3 objects to be
cached forever, and should be loaded from Cache and should never connect
to server back.