A serious question because I don't know the answer. Would the higher alcohol levels and the change in pH mean that conditions would be a bit harder for other bacteria anyway?
Yes your right it does make it less hospitable , but not imposable.
First lets have look at what could be in your unboiled/non-filtered tap water
http://dwi.defra.gov.uk/consumers/advice-leaflets/standards.pdf
The best you do is sanitize things.
In a home setting were unable to have sterile conditions (Autoclave etc). homebrewed beer will always have some amount of unwanted micro-organisms (bacteria, wild yeast, etc.)
Unwanted micro-organisms can create noticeable off-flavours. A small amount of bacteria/wild yeast will not be able to produce a noticeable off-flavour. So with being as clean as possible you should be fine.
infection is of greatest concern is during the wort phase (or right out off the kit). When there is wort, which is basically just sugar water.
The beer that you bottle only has the food of priming sugar available to micro-organisms for a short period of time (the two/three week carbonation time). After that, there is no food for either the beer yeast or the micro-organisms to consume. There is a caveat that there are some food sources (e.g., starch) which can be consumed by some bacteria that the beer yeast will not use. If the micro-organism level is low then this would not result in noticeable off-flavours.
(info from hombrewtalk)
micro-organism out compete the ones before.
(1 to 7 days) Enteric Bacteria and Kloeckera Apiculata
(2 weeks +) Saccharomyces ( wild yeast / dorment yeast)
(3 to 4 months) Lactic Acid Bacteria
(6 months) Brettanomyces plus Pichia, Candida, Hansenula and Cryptococcus
But when it comes to long term storage of homebrewed beers the largest concern is oxidation.
so you should be fine if your as clean as possible.