Oh wow at least you got that off your chest on here.Yes I agree its more reasons not excuses.
Some women can be quite embarrassed about their bodies and maybe also take a little longer to "get going", your wife obviously knows how to relax herself ready for great sex with you and has got into this habit.
I used to be exactly the same, as I was quite a shy person I had a routine and if my OH tried to change that routine it made me almost panic as I wasnt ready. I knew what turned me on.He always instigated sex every time as he was always way more experienced that I was, so it was easier.
But as i got older my hormones have gone mad, now its reversed, yay something great from hormones.
I think you have to talk to your wife some more you obviously love her, dont dismiss her "excuses" ?The maybe deeper than you think.
She may have some body issues, us girls always have them, but some more than others. But as Ive got older I have got alot more open and have talked to my OH, I really wish I had talked many years ago, i feel Ive wasted so many years.
Communication is vital in any relationship but often sex can be an awkward one with so many reasons.Try bringing up subjects of fantasies, maybe some roleplay ideas that you may want to try , ask her if she has any and maybe then mention you would love it one day if she surprised you, wearing something sexy. Does she like dresssing up, maybe say youd love it if you get home from work and find her dressed up in a naughty maids outfit or something similar.
Maybe try some sexy games from lovehoney , most of them you pick a card and have to do what that card says to the other person, there are so many varieties, that way its the cards telling her what to do (or something similar). The games warm things up and encouarge you to try new things.You also lose a bit of shyness as the game has told you to do that....touch the others nipples etc.
Have a look here and see what you think may suit the pair of you.
http://www.lovehoney.co.uk/fun/sex-games/
Im sure youl get plenty of advice on here , dont get angry its obvious you love her, and maybe they are not just excuses, they are obviously important to her.Hope this helped a bit.