Well you're initial fault is comparing it to Dawn of War or Supreme Commander. Neither can really stack up, and both are fairly different from Starcraft, (Supreme Commander is closer but not that much). Plain and simple Starcraft has one thing that sets it apart from most RTS's. That is balance. Dawn of War and Supreme Commander are frankly not balanced.
With Starcraft and Starcraft II there are not just units to throw at your enemy, there are hard and soft counters. Learn these counters and learn how to apply them. The way to win in starcraft is not necessarily to outmass or get better units than your enemy. The best way to win is to correctly counter what your enemy brings out. Hard counters are your best chance at beating your enemy. They will beat the enemy with a lesser investment. Learn them, learn how to use them well. Hard counters will help you outright win fights and stay ahead in the resource battle. Soft counters are units that are for the most part superior but don't have a distinct advantage over the unit they are fighting against, aside from being frankly better. Learn good hard and soft counters to whatever your opponent throws at you.
Secondly, scout your enemy. Know what they are up to. Don't wait until they are throwing zealots or roaches at you to begin countering. Find what they are building and try to predict the force they will send. Scouting is where most players come up short. They don't do enough and end up getting hammered before they know what is happening.
Third, and possibly most important. The game won't just be won by the proxy battles that occur outside of bases, they are usually decided by the winner's ability to recover from these battles due to out resourcing their enemy. This isn't just straight up getting more minerals or vespene than your opponent, but using counters to correctly win battles with minimal resource hit. Or fighting a superior force and causing massive damage despite being outclassed. Most importantly HARASS their workers. If their workers are dead they can't mine, if their workers are running they can't mine, for each worker you kill, for each expansion you deny that is money your enemy is wasting that they could be using on military units. It's like taking cash and tossing it into a fire.
I would also recommend that you practice micromanaging units when you fight. Don't just send them in and let them go. Learn to get the most out of each and every unit by helping them every step of the way. When two equal opponents face each other it is usually the one who micromanages the best that will win.
This will take some practice, but if you can become even simply competent with these tactics and either become a defensive or aggressive player, you will beat 80% of the people you play. Teching won't necessarily win you fights. You can play as the protoss and get 15 Colossi on the field and have them advance on your enemy, but if they hard counter them with air units that will pound them without taking damage you will take not only a massive resource hit but also a massive military hit. You have to find a good system that you are comfortable with, and alter it to best your opponent. You will lose a lot. A LOT. However, once you get your technique down you will turn the tables on your opponents and lay some smackdowns. There are very few games in the world that will give you the adrenline rush that you will feel in a really good Starcraft multiplayer match where not only every unit matters, but every unit could be the difference between you winning the match and you losing the match. Every worker killed is not just minerals but time. Every building lain to waste is precious minerals down the drain. And when you win these battles you feel like you really accomplished something awesome. Even when you lose you can walk away saying to yourself I did a damn fine job.
But like many have said learn from your replays, find mistakes not only that you made but that your opponents make. Every mistake made is a lesson to learn, every match lost is not a failure but a missed opportunity. Learn from the past lest you repeat it.
I hope this is helpful, be patient, practice, learn. And you will become the one who lays smackdowns on people.